Firm solutions
By firm solutions the homogeneous crystal phases of variable structure name.
The firm solutions of the certain structure represent one crystal phase, which structure in the certain limits (in so-called area гомогенности) can change without occurrence of new phases. Distinguish some types of firm solutions (fig. 10). Two types firm solutions of replacement (firm solutions I of a sort) and firm solutions of introduction (firm solutions II of a sort) are formed at introduction in a lattice ("dissolution" in a lattice) any of crystal connection of atoms or ions of other connection. And at education of firm solutions of replacement the "own" atoms of the basic substance (matrix) are replaced on taking root atoms, and at education of firm solutions of introduction these atoms settle down in междоузлиях of a lattice of matrix substance. The third type of firm solutions is not connected to introduction in a lattice of extraneous atoms or ions, and is caused by a deviation(rejection) in the certain limits of structure of the given connection from it(him) стехиометрического of structure. Such firm solutions are called as defects нестехиометрии (for some of them sometimes use the name firm solutions of subtraction).
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Fig. 10. Types of firm solutions: and - replacement; - introduction; in - subtraction
The firm solutions are not any exclusive phenomenon. On the contrary, this rather characteristic condition of real substances, as does not exist of substances absolutely insoluble in each other in a firm condition. Precisely as practically there are no connections with coordination lattices, which structure always precisely would correspond(meet) стехиометрическому to structure.
Firm solutions of replacement. If atoms or the ions of one substance, taking root in a lattice of other substance, replace his(its) own atoms or ions in units of a lattice, there are firm solutions of replacement.
As firm solutions of replacement such solutions are called which are formed as a result of statistical replacement of atoms or ions in structure any of crystal substance (solvents or matrixes) atoms or ions of other (dissolved) substance borrowing(occupying) as a result of it regular units of a crystal lattice.
The firm solutions of replacement (fig. 10, а) often name also by mixed crystals and изоморфными by mixes, and process of education of firm solutions of replacement name изоморфным by replacement.
At education of firm solutions of replacement basically to replace each other can both катионы, and анионы.
Some substances can form firm solutions rather easily, for example at their joint кристаллизации of solutions. However more often, for example in силикатных systems, educations of firm solutions need significant energy of activation, therefore their occurrence is connected to various thermal processes (heating to high temperature, плавлением with subsequent кристаллизацией, гидротермальными by processes).
The quantity(amount) of extraneous atoms or ions which are taking root in structure of the basic substance, can be various. Some substances can mix up among themselves over a wide range, down to complete replacement of own atoms with atoms of other substance. In this case speak about a continuous number(line) of firm solutions, complete смешиваемости or accomplished(perfect) изоморфизме. To such substances, for example, the forming continuous firm solutions - оливины concern 2МgO·SiO2 and 2FеО-SiO2. And in structure 2FеО·SiO2 катионы of iron can be completely replaced on катионы магния and, on the contrary, in structure 2МgO·SiO2 катионы магния on катионы of iron (replacement such as Мg2 +-Fе2 +). Replacements quantitatively however are much more often can occur only in the certain limits, outside of which the firm solutions are not formed any more. In this case speak about the limited number(line) твер д ы х of solutions limited смешиваемости or imperfect изоморфизме (at very small solubility education of firm solutions name эндокриптией - masking).
Ability of atoms or ions to enter into structure of other substance is defined(determined), on the one hand, by individual properties of atoms or ions (size, charge, electronic structure) and, on the other hand, by features of crystal structure of substances forming firm solutions.
Firm solutions of introduction. The atoms or ions of one substance can not replace atoms or ions another, and to settle down in intervals between them (fig. 10, б). In this case there are firm solutions of introduction.
As firm solutions of introduction such solutions are called which are formed as a result of introduction of atoms or ions of one substance in free intervals (междоузлия) of a crystal lattice of other substance - solvent.
The typical representatives of similar firm solutions are the so-called phases of introduction - connections formed at introduction in междоузлия плотноупакованных of lattices of transitive metals of atoms неметаллов, for example of hydrogen (гидриды), nitrogen (нитриды), carbon (карбиды) and т. д. A concrete example of a phase of introduction is the steel - firm solution of introduction of carbon in a lattice of iron. The phases of introduction of variable structure often have significant areas гомогенности.
It is necessary to note, that the firm solutions of introduction as against firm solutions of replacement can be only limited, as it is usual at the certain concentration растворяющегося of a component of a pressure(voltage) in a lattice at the expense of taking root atoms become so significant, that the existence of a steady firm solution is poorly probable.
Many properties of phases of introduction, such, for example, as high hardness and тугоплавкость, exceeding these characteristics at metals, are caused strong ковалентной by communication(connection) of atoms of metal and неметалла with participation -электронов. The presence of metal internuclear communication(connection) in similar phases explains their metal shine, high electrical conductivity, ability of some of them near to temperature of absolute zero to pass in сверхпроводящее a condition.
Defects нестехиометрии. Now is established, that practically all chemical connections in a firm condition with coordination (nuclear, ионными or metal) lattices have variable structure, т. е. Find out to some extent deviations(rejection) from стехиометрического of structure expressed by the formula of this connection. The area of structures laying inside boundary meanings(importance) of infringement стехиометрического of structure, is called as area гомогенности or area нестехиометрии. Constant and constant chemical structure appropriate стехиометрической to the formula, can have only connections with molecular lattices.
The deviations(rejection) from стехиометрии are a consequence of defects of a lattice (defects нестехиометрии), which can be shown as surplus (in comparison with стехиометрическим) катионов owing to анионных of vacancies (КС1, ТhO2, СеO2, РbО, ТiO and т. д.) or as a result of presence катионов in междоузлиях of a lattice (ZnО, СdO and т. д.), surplus анионов because of presence in a lattice катионных of vacancies (FеО, NiO, FеS, ТiO and т. д.) or presence анионов in междоузлиях (UO2 and т. д.). The combinations of the specified kinds of defects in the same connection are possible(probable) also.
return false">ссылка скрытаAs нестехиометрические of connection within the limits of area гомогенности represent one phase of variable structure, they can be qualified as firm solutions. If the infringements стехиометрии are called by presence in a lattice катионных or анионных of vacancies, т. е. At lack of atoms in appropriate катионной or анионной подрешетке, such firm solutions sometimes name by firm solutions of subtraction (fig. 10, е), if these infringements are called by surplus катионов or анионов in междоузлиях, such firm solutions can be considered(examined) as firm solutions of introduction own катионов or анионов of the given connection in his(its) crystal lattice.
The occurrence нестехиометрических of connections is a consequence термодинамически of an inevitable exchange of substance of the given crystal phase with an environment, т. е. By other phases (газообразными, liquid or firm). The degree of a deviation(rejection) from стехиометрии depends first of all on a физико-chemical nature of the connection and for different connections is various. Sometimes area гомогенности (area нестехиометрии) happens rather narrow and its(her) detection is limited to unsufficient sensitivity of used methods of research. Such connections can conditionally be considered(examined) as connection not having areas гомогенности, т. е. Connections of constant structure. Them sometimes name by linear phases, as on the diagram of a condition the structure of these connections is displayed by a vertical line - ordinate of the appropriate structure.