Polymorphism and PolymerCrystallite Concept
of Glass Structure

V. S. Minaev

OAO Elma, Materials Science Research Institute, Moscow, 103460 Russia

Abstract—The “polymer–crystallite” concept, involving the main aspects of the Lebedev crystallite theory and
the Zachariasen random network model, was most completely formulated by E.A. Porai-Koshits in the 1950s.
According to this concept, a glass can be represented as a polymeric continuous three-dimensional network in
which the atomic arrangement exhibits different degrees of order. The regions with the highest degree of order
are the crystallites—extremely tiny crystals consisting of a very small number of unit cells. The data indicating
the absence of the finest crystalline inclusions in a well-produced glass, and also an increasing number of spec-
troscopic (Galeener) and diffraction (Porai-Koshits, Gerber, and Golubkov) investigations demonstrating the
effect of different crystalline polymorphic modifications on the structure of a glass-forming material, allow one
to advance the ideas of the polymer–crystallite structure into the concept of the polymeric polymorphic–crys-
talloid structure of glasses. In this case, crystallites characterized by a limited long-range order are modified
into crystalloids (structural fragments of different crystalline polymorphic modifications) without long-range
order, and the notion of polymerization is extended to the notion of polymorphic polymerization—the process
involving the above crystalloids. The structure of glasses and glass-forming liquids, variations in their proper-
ties, relaxation processes occurring in them, the nature of the glass transition, and the glass transition tempera-
ture T_g are determined by the concentration ratio between crystalloids of different polymorphic modifications
and its variation depending on the external conditions (temperature T, pressure P, etc.).

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