IN gaseous the state of the molecules of a substance are at a sufficiently large distance from each other and occupy a small volume of the substance. In the gaseous state, the molecules or atoms that make up the gas practically do not interact with each other. The structure of gaseous substances is not ordered.

When gaseous substances condense, they form liquid substances. In the liquid state, the distance between the molecules is much smaller, and the bulk of the volume of the substance is occupied by molecules, in contact with each other and attracted to each other. Those. in the liquid state, some ordering of the particles is observed, the short-range order is observed.

IN solid particles are so close to each other that strong bonds arise between them, there is practically no movement of particles relative to each other. There is a high degree of order in the structure. Solids may be in amorphous and crystalline condition.

Amorphous substances do not have an ordered structure; like liquids, they have only a close order (glassy state). Amorphous substances are fluid. Polymers, resins, amorphous silicon, amorphous selenium, fine silver, amorphous silicon oxide, germanium, some sulfates, carbonates are in an amorphous state. Amorphous substances are isotropic, i.e. physical properties substances spread equally in different directions, and they do not have a strictly defined melting point, they melt in a certain temperature range. But the vast majority of solids are crystalline substances.

Crystalline substances are characterized by long-range order, i.e. three-dimensional periodicity of the structure throughout the volume. The regular arrangement of particles is depicted as crystal lattices, at the nodes of which are particles that form a solid. They are connected by imaginary lines.

Ideal single crystals have:

Anisotropy - i.e. in different directions in the volume of the crystal, the physical properties are different.

certain melting point.

Crystalline substances are characterized by the energy of the crystal lattice, this is the energy that must be spent to destroy the crystal lattice and remove particles from the interaction.

The lattice constant characterizes the distance between particles in the crystal lattice, as well as the nodes between the faces of the crystal lattice.

The coordination number of a crystal lattice is the number of particles directly adjacent to a given particle.

The smallest structural unit is the elementary cell. There are seven types of crystal lattices: cubic, tetrahedral, hexagonal, rhombohedral, orthorhombohedral, monoclinic and triclinic.

They differ from each other by the angles between the axes (a, b, g) and the lattice constants (a, b, c).

There are various substances that crystallize in the same crystal lattices - isomorphic substances.

Example: KAl(SO 4) 2 × 12H 2 O and KCr(SO 4) 2 × 12H 2 O

According to the type of particles in the nodes of the crystal lattice, crystals are: molecular, atomic - covalent, ionic, metallic and mixed.

1). Molecular crystals: at the nodes are molecules between which there are van der Waals interactions or hydrogen bonds. There are very few substances with a molecular lattice. These include non-metals, with the exception of carbon and silicon, all organic compounds with non-ionic bonds, and many inorganic substances. For example, the structure of ice:

3). Ionic crystals: at the nodes are ions that are held near each other due to electrostatic interaction. Ionic compounds include most salts and a small number of oxides. Ionic compounds have relatively high melting points. Due to the fact that the ionic bond is unsaturated and non-directional, the ionic lattice is characterized by high coordination numbers (6.8).

4). There are metal crystals. Metal gratings form simple substances Most of the elements in the periodic table are metals. In terms of strength, metal lattices are between atomic and molecular crystal lattices.

5). Mixed crystals are often found in nature, in which the interaction is carried out by both covalent and van der Waals interactions, for example, graphite:

There is a covalent bond in the layers (sp 2 hybridization of the carbon atom), between the layers there is a van der Waals interaction.

Some substances can crystallize into different crystal lattices. This phenomenon is called polymorphism (examples are: carbon, diamond and graphite) or allotropy .

A natural difference in the structure of most solid materials (with the exception of single crystals), in comparison with liquid and especially gaseous (low molecular weight) substances, is their more complex multilevel organization (see Table 4.1 and Fig. 4.3). This is due to a decrease in covalence and an increase in the metallicity and ionicity of homo- and heteronuclear bonds of the elements of their microstructure (see Figs. 6.2 and 6.6 and Tables 6.1-6.7), which leads to an increase in the number of elements in the structure of matter and material and a corresponding change its aggregate state. When studying the structural hierarchy of solid materials, it is necessary to understand the unity and differences in the levels of structural organization of solid metallic and non-metallic materials, taking into account the degree of order in the volume of the material of the elements that form them. Special meaning has a difference in the structure of solid crystalline and amorphous bodies, which consists in the ability of crystalline materials, unlike amorphous bodies, to form a number of more complex structures than the basic electron-nuclear chemical level of structures.

amorphous state. The specificity of the amorphous (translated from Greek - formless) state lies in the presence of a substance in condensed (liquid or solid) state with the absence in its structure of three-dimensional periodicity in the arrangement of elements (atomic cores or molecules) that make up this substance. As a result, the features of the amorphous state are due to the absence long-range order - strict repetition in all directions of the same structural element (nucleus or atomic core, group of atomic cores, molecules, etc.) over hundreds and thousands of periods. At the same time, the substance in the amorphous state has short range order- consistency in the arrangement of neighboring elements of the structure, i.e. an order observed at distances comparable to the size of the molecules. With distance, this consistency decreases and disappears after 0.5-1 nm. Amorphous substances differ from crystalline ones in isotropy, i.e. like a liquid they have the same meaning given property when measured in any direction within a substance. The transition of an amorphous substance from a solid to a liquid state is not accompanied by an abrupt change in properties - this is the second important feature that distinguishes the amorphous state of a solid from the crystalline state. Unlike a crystalline substance, which has a certain melting point, at which an abrupt change in properties occurs, an amorphous substance is characterized by a softening interval and a continuous change in properties.

Amorphous substances are less stable than crystalline ones. Any amorphous substance should, in principle, crystallize over time, and this process should be exothermic. Often, amorphous and crystalline forms are different states of the same chemical substance or material in composition. Thus, amorphous forms of a number of homonuclear substances (sulfur, selenium, etc.), oxides (B 2 O e, Si0 2, Ge0 2, etc.) are known.

However, many amorphous materials, in particular most organic polymers, cannot be crystallized. In practice, crystallization of amorphous, especially high-molecular, substances is observed very rarely, since structural changes are inhibited due to the high viscosity of these substances. Therefore, if you do not resort to special methods, such as long-term high-temperature exposure, the transition to the crystalline state proceeds at an extremely low rate. In such cases, we can assume that the substance in the amorphous state is almost completely stable.

Unlike the amorphous state inherent in substances that are both in liquid or molten form, and in solid condensed form, glassy state only applies to hard state of aggregation substances. As a result, in liquid or molten substances can be in the amorphous state with any preferred type of connection(covalent, metallic and ionic) and, therefore, with molecular and non-molecular structure. However in solid amorphous, or more precisely, glassy state will primarily be HMC-based substances characterized predominantly covalent bond type elements in chains of macromolecules. This is due to the fact that the solid amorphous state of a substance is obtained as a result of supercooling of its liquid state, which prevents crystallization processes and leads to “freezing” of the structure with a short-range order of elements. Note that the presence of macromolecules in the structure of polymeric materials due to the influence of the steric-size factor (after all, it is easier to create a crystal from cations than from molecules) leads to an additional complication of the crystallization process. Therefore, organic (polymethyl methacrylate, etc.) and inorganic (oxides of silicon, phosphorus, boron, etc.) polymers are capable of forming glasses or realizing an amorphous state in solid materials. True, today metal melts at ultra-high cooling rates (>10 6 °C/s) are transferred to an amorphous state, obtaining amorphous metals or metal glass with a set of new valuable properties.

crystalline state. In a crystalline body, it is observed as near, and long range order arrangement of structural elements (atomic cores or particles in the form of individual molecules), i.e. elements of the structure are placed in space at a certain distance from each other in a geometrically correct order, forming crystals - solid bodies that have natural form regular polyhedra. This shape is a consequence of the ordered arrangement of elements in the crystal, which form a three-dimensionally periodic spatial stacking in the form crystal lattice. A substance in a crystalline state is characterized by periodic repetition in three dimensions of the arrangement of atomic cores or molecules in its nodes. A crystal is an equilibrium state of solids. Each chemical substance that is under given thermodynamic conditions (temperature, pressure) in a crystalline state corresponds to a certain crystalline covalent or molecular, metallic and ionic structure. Crystals have one or another structural symmetry of atomic cores (cations in a metal or cations and anions in ionic crystals) or molecules, the corresponding macroscopic symmetry of the external form, as well as anisotropy of properties. Anisotropy - this is the dissimilarity of the properties (mechanical, physical, chemical) of a single crystal in different directions of its crystal lattice. Isotropy - This is the sameness of the properties of a substance in its various directions. Naturally, these patterns of change in the properties of a substance are determined by the specifics of the change or non-change in their structure. Real crystalline materials (including metals) are quasi-isotropic structures, those. they are isotropic at the mesostructural level (see Table 4.1) and their properties are the same in all directions. This is because most natural or artificial crystalline materials are polycrystalline substances, not single crystals

(like a diamond). They consist of a large number so-called grains or crystallites, whose crystallographic planes are rotated relative to each other through a certain angle a. In this case, in any direction of the mesostructure of the material, there are approximately the same number of grains with different orientations of crystallographic planes, which leads to independence of its properties from the direction. Each grain consists of individual elements - blocks that are rotated relative to each other at angles of the order of several minutes, which also ensures the isotropy of the properties of the grain itself as a whole.

Crystalline states of the same substance can differ in structure and properties, and then they say that this substance exists in various modifications. The existence of several crystalline modifications in a given substance is called polymorphism, and the transition from one modification to another - polymorphic transformation. Unlike polymorphism, allotropy- this is the existence of an element in the form of various "simple" (or, more precisely, homonuclear) substances, regardless of their phase state. For example, oxygen 0 2 and ozone O e are allotropic forms of oxygen that exist in gaseous, liquid and crystalline states. At the same time, diamond and graphite - allotropic forms of carbon - are simultaneously its crystalline modifications, in this case the concepts of "allotropy" and "polymorphism" coincide for its crystalline forms.

Often there is also a phenomenon isomorphism, in which two substances of different nature form crystals of the same structure. Such substances can replace each other in the crystal lattice, forming mixed crystals. For the first time, the phenomenon of isomorphism was demonstrated by the German mineralogist E. Mitscherlich in 1819 using the example of KH 2 P0 4, KH 2 As0 4 and NH 4 H 2 P0 4. Mixed crystals are perfectly homogeneous mixtures of solids - these are substitutional solid solutions. Therefore, we can say that isomorphism is the ability to form substitutional solid solutions.

Traditionally, crystal structures are traditionally divided into homodesmic (coordination) and heterodesmic. homo-desmic structure have, for example, diamond, alkali metal halides. However, more often crystalline substances have heterodesmic structure; her characteristic- the presence of structural fragments, within which the atomic cores are connected by the strongest (usually covalent) bonds. These fragments can be finite groupings of elements, chains, layers, frames. Accordingly, island, chain, layered and frame structures are distinguished. Almost all organic compounds and inorganic substances such as halogens, 0 2, N 2, CO 2, N 2 0 4, etc. have island structures. Molecules play the role of islands, therefore such crystals are called molecular. Often polyatomic ions (for example, sulfates, nitrates, carbonates) act as islands. For example, crystals of one of the Se modifications (the atomic cores are connected in endless spirals) or PdCl 2 crystals, which contain endless ribbons, have a chain structure; layered structure - graphite, BN, MoS 2, etc.; the frame structure is CaTYu 3 (the atomic cores of Ti and O, united by covalent bonds, form an openwork frame, in the voids of which the atomic cores of Ca are located). Some of these structures are classified as inorganic (carbon-free) polymers.

According to the nature of the bond between atomic cores (in the case of homodesmic structures) or between structural fragments (in the case of heterodesmic structures), there are distinguished: covalent (for example, SiC, diamond), ionic, metallic (metals and intermetallic compounds) and molecular crystals. Crystals of the last group, in which the structural fragments are linked by intermolecular interaction, have the largest number of representatives.

For covalent single crystals such as diamond, carborundum, etc. are characterized by refractoriness, high hardness and wear resistance, which is a consequence of the strength and direction of the covalent bond in combination with their three-dimensional spatial structure (polymer bodies).

Ionic crystals are formations in which the adhesion of microstructure elements in the form of counterions is due mainly to ionic chemical bonds. An example of ionic crystals are the halides of alkali and alkaline earth metals, in the crystal lattice sites of which there are alternating positively charged metal cations and negatively charged halogen anions (Na + Cl -, Cs + Cl -, Ca + F^, Fig. 7.1).

Rice. 7.1.

IN metal crystals the adhesion of atomic cores in the form of metal cations is due predominantly to metallic non-directional chemical bonds. This type of crystals is characteristic of metals and their alloys. At the nodes of the crystal lattice there are atomic cores (cations) interconnected by OE (electron gas). The structure of metallic crystalline bodies will be discussed in more detail below.

molecular crystals are formed from molecules linked to each other by van der Waals forces or hydrogen bonds. A stronger covalent bond acts inside the molecules (C to prevails over C and and C m). Phase transformations of molecular crystals (melting, sublimation, polymorphic transitions) occur, as a rule, without the destruction of individual molecules. Most molecular crystals are crystals of organic compounds (eg naphthalene). Molecular crystals also form substances such as H 2, halogens of the type J 2, N 2, 0 2, S g, binary compounds of the type H 2 0, CO 2, N 2 0 4, organometallic compounds and some complex compounds. Molecular crystals also include crystals of such natural polymers as proteins (Fig. 7.2) and nucleic acids.

Polymers, as already mentioned above, as a rule, also refer to substances that form molecular crystals. However, in the case when the packing of macromolecules has a folded or fibrillar conformation, it would be more correct to speak of covalent molecular crystals(Fig. 7.3).

Rice. 7.2.

Rice. 7.3.

This is due to the fact that along one of the lattice periods (for example, the period With in the case of polyethylene, the macromolecules of which are in a folded conformation, forming a lamella), strong chemical (Fig. 7.3), mainly covalent, bonds act. At the same time, along two other lattice periods (for example, periods b And With in the same folded polyethylene crystals), already weaker forces of intermolecular interaction act.

The division of crystals into these groups is largely arbitrary, since there are gradual transitions from one group to another as the nature of the bond in the crystal changes. For example, among intermetallic compounds - compounds of metals with each other - one can distinguish a group of compounds in which a decrease in the metal component chemical bond and the corresponding growth of the covalent and ionic components lead to the formation of cholesterol in accordance with the classical valencies. Examples of such compounds are magnesium compounds with elements main subgroup IV and V groups Periodic system, which are transitional between metals and non-metals (Mg 2 Si, Mg 2 Ge, Mg 2 Sn, Mg 2 Pb, Mg 3 As 2, Mg 3 Sb 7, Mg 3 Bi 7), to the main characteristic features which are usually referred to as:

• their heteronuclear crystal lattice differs from the homonuclear lattices of the parent compounds;
• in their connection, a simple multiple ratio of components is usually preserved, which makes it possible to express their composition by a simple formula A sh B;? , where A and B are the corresponding elements; T And P - prime numbers;
• heteronuclear compounds are characterized by a new quality of structure and properties, in contrast to the original compounds.

in crystal structural elements(ions, atomic cores, molecules) that form a crystal are arranged regularly in different directions (Fig. 7 La). Usually, a spatial image of the structure of crystals is presented schematically (Fig. 7.45), marking the centers of gravity of structural elements, including lattice characteristics, with dots.

Planes parallel to the coordinate planes that are at a distance a, b, c from each other, divide the crystal into many equal and parallel oriented parallelepipeds. The smallest of them is called elementary cell, their combination forms a spatial crystal lattice. The vertices of the parallelepiped are the nodes of the spatial lattice; the centers of gravity of the elements from which the crystal is built coincide with these nodes.

Spatial crystal lattices completely describe the structure of a crystal. To describe the unit cell of the crystal lattice, six quantities are used: three segments equal to the distances to the nearest elementary particles along the coordinate axes a, b, c, and three angles between these segments a, (3, y.

The ratios between these quantities determine the shape of the cell, depending on which all crystals are divided into seven systems (Table 7.1).

The size of the unit cell of the crystal lattice is estimated by the segments a, b, s. They are called lattice periods. Knowing the lattice periods, it is possible to determine the radius of the atomic core of an element. This radius is equal to half of the smallest distance between particles in the lattice.

The degree of complexity of the lattice is judged by the number of structural elements, per one elementary cell. In a simple spatial lattice (see Fig. 7.4), there is always one element per cell. Each cell has eight vertices, but

Rice. 7.4. Arrangement of elements in a crystal: A- image with the placement of the volume of the atomic core of the element; b - spatial image of an elementary cell and its parameters

Table 7.1

Characteristics of crystalline systems

each element at the top refers, in turn, to eight cells. Thus, from the node to the share of each cell there is V 8 volume, and there are eight nodes in the cell, and, therefore, there is one structural element per cell.

In complex spatial lattices, there is always more than one structural element per cell, which are most common in the most important pure metal compounds (Fig. 7.5).

The following metals crystallize in the bcc lattice: Fe a, W, V, Cr, Li, Na, K, etc. Fe y, Ni, Co a, Cu, Pb, Pt, Au, Ag, etc. crystallize in the fcc lattice. Mg, Ti a, Co p, Cd, Zn, etc. crystallize in the hcp lattice.

System, period and number of structural elements, per unit cell make it possible to fully represent the location of the latter in the crystal. In some cases, additional characteristics of the crystal lattice are used, due to its geometry and reflecting the packing density of the element

Rice. 7.5. Types of complex elementary cells of crystal lattices: A - BCC; 6 - HCC; V- hcp of tare particles in a crystal. These characteristics are CF and compactness factor.

The number of nearest equidistant elementary particles determines coordination number. For example, for a simple cubic lattice, the CF will be 6 (Kb); in the lattice of a body-centered cube (bcc) for each atomic core, the number of such neighbors will be equal to eight (K8); for a face-centered cubic lattice (fcc), the CF number is 12 (K 12).

The ratio of the volume of all elementary particles per one elementary cell to the entire volume of the elementary cell determines compactness factor. For a simple cubic lattice, this coefficient is 0.52, for bcc - 0.68 and fcc - 0.74.

• Sirotkin R.O. The effect of morphology on the yield behavior of solution crystallizedpolyethylenes: PhD thesis, University of North London. - London, 2001.

The vast majority of solids in nature have a crystalline structure. So, for example, almost all minerals and all metals in the solid state are crystals.

A characteristic feature of the crystalline state, which distinguishes it from the liquid and gaseous states, is the presence anisotropy, i.e., the dependence of a number of physical properties (mechanical, thermal, electrical, optical) on the direction.

Bodies whose properties are the same in all directions are called isotropic. Isotropic, except for gases and, with some exceptions, all liquids, are also amorphous solids. The latter are supercooled liquids.

The reason for the anisotropy of crystals is the ordered arrangement of particles (atoms or molecules) from which they are built. The ordered arrangement of particles is manifested in the correct external faceting of crystals. Crystals are limited by flat faces intersecting at certain angles, determined for each given kind of crystals. Cleavage of crystals occurs more easily along certain planes, called cleavage planes.

The correctness of the geometric shape and the anisotropy of crystals usually do not manifest themselves for the reason that crystalline bodies usually occur in the form polycrystals, i.e., conglomerates of a multitude of randomly oriented small crystals fused together. In polycrystals, anisotropy is observed only within the limits of each individual crystal, while the body as a whole does not exhibit anisotropy due to the random orientation of the crystals. By creating special conditions for crystallization from a melt or solution, large single crystals can be obtained - single crystals any substance. Single crystals of some minerals are found in nature in their natural state.

The ordering of the arrangement of the atoms of a crystal lies in the fact that the atoms (or molecules) are located at the nodes of a geometrically regular spatial lattice. The whole crystal can be obtained by repeatedly repeating in three different directions the same structural element, called elementary crystal cell(Fig. 110.1, A). Rib lengths a, b And With crystal cell are called periods of identity crystal.

The crystal cell is a parallelepiped built on three vectors A , b , With , whose moduli are equal to the identity periods. This parallelepiped, except for the edges A,b, With, it is also characterized by the angles α, β and γ between the ribs (Fig. 110.1, b). The values A,b, With and α, β, γ uniquely determine the elementary cell and are called its parameters.

The elementary cell can be selected in various ways. This is shown in fig. 110.2 on the example of a flat structure. Wall cladding with alternating light and dark triangular tiles can be obtained by multiple repetition in two directions of different cells (see, for example, cells 1 , 2 and 3; arrows indicate n directions in which cells are repeated). cells 1 And 2 differ in that they include a minimum number of structural elements (one light and one dark tile). The crystalline cell, which includes the smallest number of atoms that characterize the chemical composition of a crystalline substance (for example, one oxygen atom and two hydrogen atoms for an ice crystal), is called primitive cell. However, usually, instead of a primitive one, an elementary cell is chosen with a large number of atoms, but having the same symmetry as the entire crystal as a whole. So, shown in Fig. 110.2 a planar structure coincides with itself when rotated through 120° about any axis perpendicular to it passing through the tops of the tiles. The elementary cell has the same property 3. cells 1 and 2 have a lesser degree of symmetry: they coincide with themselves only when rotated through 360°.

). In the crystalline state, there is also a short-range order, which is characterized by constant coordinates. numbers, and lengths of chemical. connections. The invariance of the characteristics of the short-range order in the crystalline state leads to the coincidence of the structural cells during their translational displacement and the formation of a three-dimensional periodicity of the structure (see . . ). Due to its max. orderliness crystalline state in-va is characterized by a minimum. internal energy and is a thermodynamically equilibrium state for given parameters - pressure, m-re, composition (in the case), etc. Strictly speaking, a completely ordered crystalline state cannot really be. carried out, the approach to it takes place when the t-ry tends to OK (the so-called ideal). Real bodies in a crystalline state always contain a certain number of , violating both short-range and long-range order. Especially observed in solid solutions, in which individual particles and their groupings statistically occupy decomp. positions in space. Due to the three-dimensional periodicity of the atomic structure, the main features are uniformity and St-in and, which is expressed, in particular, in the fact that under certain conditions the formations take the form of polyhedra (see). Some St. Islands on the surface and near it are significantly different from these St. inside, in particular because of the violation. The composition and, accordingly, St. Islands change in volume due to the inevitable change in the composition of the medium as it grows. Thus, the homogeneity of St.-in, as well as the presence of long-range order, refers to the characteristics of the "ideal" crystalline state. Most bodies in the crystalline state are polycrystalline and are intergrowths a large number small crystallites (grains) - sections with a size of the order of 10 -1 -10 -3 mm, irregular shape and differently oriented. The grains are separated from each other by intergranular layers, in which the order of the particles is disturbed. In the intergranular layers, the concentration of impurities also occurs in the process. Due to the random orientation of the grains, polycrystalline. the body as a whole (a volume containing a sufficiently large number of grains) m. b. isotropic, eg. obtained with crystalline. with the last . However, usually in the process and especially plastic. there is a texture - advantages, the orientation of the crystal. grains in a certain direction, leading to St. in. On a one-component system, due to the crystalline state, several can respond. fields located in an area of ​​relatively low temp. and raise . If there is only one state and the substance does not chemically decompose with increasing t-ry, then the states border on fields and along the lines and - respectively, and () can be in a metastable (supercooled) state into states, while the crystalline state cannot be in the field or, i.e., crystalline. in-in it is impossible to overheat above t-ry or. Some-rye in-va (mesogens) when heated, they turn into liquid crystals. state (see). If there are two or more states on the diagram of a one-component system, these fields border along the line of polymorphic transformations. Crystalline in-in can be overheated or supercooled below the t-ry polymorphic transformation. In this case, the considered crystalline state of the islands may be in the field of others. crystalline. modifications and is metastable. While and due to the existence of critical points on a line can be continuously converted into each other, the question of the possibility of continuous mutual transformation. crystalline state and has not been finally resolved. For some in-in, you can evaluate the critical. parameters - pressure and t-ru, at which D H pl and D V pl are equal to zero, i.e., the crystalline state and are thermodynamically indistinguishable. But really such a transformation. was not observed for any of the islands (see). In-in from the crystalline state can be transferred to a disordered state (amorphous or glassy), not corresponding to the minimum free. energy, not only a change (, t-ry, composition), but also an impact or subtle. Critical the particle size, at which it no longer makes sense to talk about the crystalline state, is approximately 1 nm, i.e. of the same order as the unit cell size. TO the crystalline state is usually distinguished from other varieties of the solid state (glassy, ​​amorphous) according to X-ray patterns of the island.
===
Use literature for the article "CRYSTAL STATE": Shaskolskaya M. P., Crystallography, M., 1976; Modern Crystallography, ed. B. K. Weinstein. vol. I. M., 1979. P. I. Fedorov.

Page "CRYSTAL STATE" prepared from materials.

It is characterized by the presence of long-range order in the arrangement of particles (atoms, ions, molecules). In K. s. there is also a short-range order, which is characterized by constant coordinates. numbers, bond angles and chemical lengths. connections. Invariance of characteristics of the short-range order in C. s. leads to the coincidence of structural cells during their translational movement and the formation of a three-dimensional periodicity of the structure (see Fig. Crystal chemistry. crystals). Due to its max. orderliness K. with. in-va is characterized by a minimum. internal energy and is a thermodynamically equilibrium state for given parameters - pressure, t-re, composition (in the case solid solutions) and others. Strictly speaking, a completely ordered K. s. really not m. b. carried out, the approach to it takes place when the t-ry tends to OK (the so-called ideal crystal). Real bodies in K. with. always contain a certain number of defects, violating both short-range and long-range order. Especially many defects are observed in solid solutions, in which individual particles and their groups statistically occupy decomp. positions in space. Due to the three-dimensional periodicity of the atomic structure, the main features of crystals are homogeneity and sv-in and symmetry, which is expressed, in particular, in the fact that under certain conditions the formations take the form of polyhedra (see Fig. Single crystal growing). Some St. Islands on the surface of the crystal and near it are significantly different from these St. Islands inside the crystal, in particular due to symmetry breaking. The composition and, accordingly, St. Islands change throughout the volume of the crystal due to the inevitable change in the composition of the medium as the crystal grows. T. arr., the homogeneity of St. in the same way as the presence of long-range order, refers to the characteristics of the "ideal" K. s. Most of the bodies in K. s. is polycrystalline and represents intergrowths of a large number of small crystallites (grains) - sections with a size of the order of 10 -1 -10 -3 mm, irregular in shape and differently oriented. The grains are separated from each other by intergranular layers, in which the order of the particles is disturbed. In the intergranular layers, the concentration of impurities also occurs in the course of crystallization. Due to the random orientation of the grains, polycrystalline. the body as a whole (a volume containing a sufficiently large number of grains) m. b. isotropic, eg. obtained by precipitation of crystalline. powders with last. sintering. However, usually in the process of crystallization and especially plastic. deformation occurs texture-advantages, orientation of the crystal. grains in a certain direction, leading to the anisotropy of St.-in. On state diagram single-component system due to polymorphism K. s. can answer several fields located in the area of ​​relatively low t-r and higher. pressure. If there is only one field K. s. and in-in chemically does not decompose with an increase in t-ry, then the field K. s. borders on the fields of liquid and gas along the lines of melting, crystallization and sublimation - condensation, respectively. cannot be in the field of a liquid or, i.e., crystalline. in-in it is impossible to overheat above the t-ry of melting or sublimation. Some-rye in-va (mesogens) when heated, they turn into liquid crystals. condition (see liquid crystals). If the diagram of a one-component system has two or more fields of condensate s., these fields border along the line of polymorphic transformations. Crystalline in-in can be overheated or supercooled below the t-ry polymorphic transformation. In this case, the considered K. s. in-va may be in the field of other crystalline. modifications and is metastable. While liquid and vapor due to the existence of critical. points on the evaporation line can be continuously converted into each other, the question of the possibility of continuous mutual transformation. K. s. and fluid is not finally resolved. For some in-in, you can evaluate the critical. the parameters are pressure and t-ru, for which DH pl and DV pl are equal to zero, i.e. K. s. and liquid are thermodynamically indistinguishable. But really such a transformation. was not observed for any of the v-va (see. Critical condition). In-in from K. with. can be transferred to a disordered state (amorphous or glassy) that does not meet the minimum free. energy, not only by changing the parameters of the state (pressure, t-ry, composition), but also by the impact ionizing radiation or fine grinding. Critical the particle size, at which it no longer makes sense to talk about K. s., is approximately 1 nm, i.e., of the same order as the size of the unit cell. K. s. usually distinguished from other varieties of the solid state (glassy, ​​amorphous) according to X-ray diffraction patterns. Lit.: Shaskolskaya M. P., Crystallography, Moscow, 1976; Modern Crystallography, ed. B. K. Weinstein. vol. I. M., 1979. P. I. Fedorov.

Chemical encyclopedia. - M.: Soviet Encyclopedia. Ed. I. L. Knunyants. 1988 .

See what the "CRYSTAL STATE" is in other dictionaries:

crystalline state- kristalinė būsena statusas T sritis chemija apibrėžtis Būsena, kai medžiagos dalelės (atomai, jonai, molekulės) išsidėsčiusios taisyklinga, visomis kryptimis periodiškai pasikartojančia tvarka. atitikmenys: engl. crystalline state rus.… … Chemijos terminų aiskinamasis žodynas

crystalline state- kristalinė būsena statusas T sritis fizika atitikmenys: angl. crystalline state vok. kristalliner Zustand, m rus. crystalline state, n pranc. état cristallin, m … Fizikos terminų žodynas

CRYSTAL STATE- the correct, regular arrangement of particles (atoms, molecules) in space, forming a crystal lattice ... Metallurgical Dictionary

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App., number of synonyms: 1 crystallized (2) ASIS Synonym Dictionary. V.N. Trishin. 2013 ... Synonym dictionary

The state of matter, when the particles that make it up (atoms, ions, molecules) occupy strictly fixed positions according to the geometric laws of spatial gr. and corresponding grids. Geological dictionary: in 2 volumes. M.: Nedra. Edited by … Geological Encyclopedia

STATE- (1) an amorphous (X-ray amorphous) state of a solid, in which there is no crystal structure (atoms and molecules are arranged randomly), it is isotropic, i.e., has the same physical. properties in all directions and does not have a clear ... ... Great Polytechnic Encyclopedia

Wiktionary has an entry for "state" State is an abstract term for a set of stable values ​​of variables ... Wikipedia

This term has other meanings, see Glass (meanings). Main article: Glass The glassy state is a solid amorphous metastable state of matter in which there is no pronounced crystal lattice, conditional elements ... ... Wikipedia

- (from Greek a negative particle and morphē form) a solid state of matter that has two features: its properties (mechanical, thermal, electrical, etc.) in natural conditions do not depend on the direction in the substance ... ... Great Soviet Encyclopedia