The development of methods for the research and synthesis of solid phases by the scientific school of Ya. A Ugai. Review

Galina V Semenova,Alexander Yu Zavrazhnov

doi:10.17308/kcmf.2021.23/3526

Abstract

The scientific school founded by Yakov A. Ugai has existed at Voronezh State University for over fifty years. One of its focus areas has been the development of physics and chemistry for obtaining solid phases in systems with volatile components. This determined the necessity to develop methods for the investigation of vapour pressure (tensimetric methods). This article only focuses on some of the works by the VSU staff dedicated to the study and construction of P-T-x diagrams. This review analyses phase equilibria and the nature of the intermediate phases in the AIV – BV, AIV – BV – СV, and AIII – BVI systems.Owing to the special nature of the cation-cation and anion-anion bonds, these compounds have highly specific properties that make them promising materials (2D materials in particular). The article presents an overview of works devoted to the construction of P-T-x diagrams and the investigation of defect formation processes in binary and ternary systems based on AIVBV compounds. It should be emphasised that the known techniques needed updating due to the high values of vapour pressure. This allowed conducting experiments at pressures of about 35-40 atmospheres. The study of the AIII - BVI systems,on the contrary, is complicated by low values of vapour pressure over indium and gallium chalcogenides and the complex composition of the vapour. For such systems the auxiliary component method was developed. The possibilities of its application are wide and are not limited to AIIIBVI compounds. A new method for nonstoichiometry regulation was developed and applied using non-destructive selective chemical transport reactions (i.e. with the participation of an auxiliary component). This method is based on the introduction or removal of one of the sample components by means of a selective chemical transport reaction. In conclusion, the development of methods for the research and synthesis of intermediate phases with variable compositions (properties) was analysed based on the example of the discussed systems.

Highlights

In 1981, Yakov Ugai was awarded with the USSR National Prize in Science and Technology for a series of studies in the area of chemical thermodynamics of semiconductors
Unique experimental units created by the department staff allowed exploring the nature of phase equilibria in complex systems with volatile components and to construct phase diagrams for such systems
It should be noted that P T x diagrams of the Ge – As, Si – As, Ge – P, and Si – As binary systems and the AIV – BV – СV ternary systems were defined with the help of manometric tensimetry, i.e. using a quartz null-manometer with a flat membrane [6 – 18]

Summary

Introduction

In 1981, Yakov Ugai was awarded with the USSR National Prize in Science and Technology for a series of studies in the area of chemical thermodynamics of semiconductors. The analysis of the obtained data in combination with the results of the study of alloys with lower tin contents allowed establishing the presence of four-phase equilibria of the peritectic type with the participation of the melt and solid solutions based on tin monoarsenide, tin phosphide SnP3, and the As P 0.6–0.7 0.4–0.3 intermediate phase. It should be noted that P T x diagrams of the Ge – As, Si – As, Ge – P, and Si – As binary systems and the AIV – BV – СV ternary systems were defined with the help of manometric tensimetry, i.e. using a quartz null-manometer with a flat membrane [6 – 18] These studies were greatly facilitated due to the absolutely incongruent nature of silicon and germanium phosphides and arsenides evaporation (sublimation), wherein only phosphorus or arsenic transit to the vapour phase mainly in the form four-atom molecules.

Calculation of partial pressures and p-T diagram

Possibility to calculate thermodynamic quantities

Conclusion