The problem of unified model of condensed state can be solved by using solid-like model of liquids. A liquid arises when in a heated crystal a universal process of microcrack formation takes place that leads to originating a great number of very small crystals: microcrystallites. In the paper the two basic notions: the effective temperature of crystal surfaces and the internal thermal stresses in crystals are discussed. These notions make possible the microcrystallite model of liquids and the unified model of condensed state. Thus, the microcracks, resulted from thermal stresses, below the melting point lead only to decreased strength of crystals but above melting point the microcracks are spread all over the crystal bulk and cause splitting of the crystal into microcrystallites that are moving freely, in short, making up a liquid. The simple relations for these processes are given. In the end of the paper the identical features of the condensed states, solid and liquid, has been considered.

Scientific bases of the general classification of crystalline materials such as single crystals, polycrystalline materials and glass ceramic have been expounded. In the systematic procedures the materials are signified by the applicability formulas. Materials belonging to the certain taxons as well as their ability to carry out some official functions under the given conditions of the relationship with the factors of the environment are also determined by the applicability formulas.

AbstractAn idea of crystal moduli (CM) as minimum aggregates for constructing of complex crystal lattices is introduced. CM arrangement in crystals is described by means of packing groups Ĝ. Twin structure constructions are demonstrated on the base of CM conception for LiNbO3, ZnS and KTiOPO4 crystals. There are next advantages of CM conception: a) Physically not verified versions of twinning appearing in other theories (Klassen‐Nekludova; Blistanov et al. 1975, 1976a) are automatically excluded; b) CM method allows to describe crystal twinning when transition strata between twin blocks appear. The connection between CM conception and crystal growth mechanism is discussed.

AbstractA concise review of Beilby's amorphous surface layers, discovered in early years of the twentieth century, is presented. While being treated mechanically the crystals form these layers characterized by an enhanced hardness and specific optical, electrical, and magnetic properties. The temperature stresses arising from a periodic contact of the abrasive with the crystal surface are supposed to be a reason for Beilby layer formation. A mathematical description of propagation of the temperature waves is given. The temperature wave amplitude is shown to be e times attenuated at the distance from the crystal surface being about the grain size.

A review of applications of optoacoustic methods, based on the pulse laser generation of the ultrasonic waves in samples studied is given. The paper demonstrates the possibilities of this method in determine the elastic, photoelastic, piezoelectric constants, optical quality and damage stability of ferro- and piezoelectrics.