Equations of state of novel solids synthesized under extreme pressure–temperature conditions

O O Kurakevych,Y Le Godec,V L Solozhenko

doi:10.1088/1742-6596/653/1/012080

Abstract

The pressure–volume–temperature equations of state have been constructed by combining experimental data and semiempirical estimations for a number of compounds recently synthesized under extreme pressure–temperature conditions. The solids with various bonding types were considered: covalent hard and superhard boron-rich and diamond-like compounds (e.g. B6O, B13N2, BP, c-BC5, and nano-cBN), ionic semiconductors (e.g. Mg2C and Mg2C3), as well as intercalation compounds (e.g. clathrates Na4Si24 and Na24+xSi136), and simple substances (e.g. boron allotropes γ-B28 and t'-B52, and open-framework silicon allotrope o-Si24 with quasi-direct bandgap). We also showed how the reliable p-V-T equations of state may be constructed using different types of data available.

Highlights

High pressure–high temperature (HPHT) large-volume synthesis allowed obtaining a number of novel materials [1] for new challenging applications as superhard [2,3,4,5,6], advanced electronic [7], photovoltaic [8] and thermoelectric [9, 10] materials, as well as superconductors [11, 12]: (i) boron allotropes [13, 14] and boron-rich compounds, (ii) superhard compounds with diamond structure; (iii) covalent clathrates of new stoichiometries (Na4−xSi24 [8, 9] and Na24+xSi136 [9, 10]) and even (iv) new unexpected semiconductors, like antifluorite Mg2C [24], dense Mg2C3 [25] and pure silicon allotrope with quasi-direct bandgap, Si24 [8]
A part of the lacking data can be replaced by fitted parameters of common models [26,27,28] or with ab initio calculations [29], the reliable p-V-T equations of state (EOS) data are crucial for that
In the present paper we describe the method of construction of such equations of state using integrated form of the Anderson-Gruneisen equation [30, 31]

Summary

Introduction

High pressure–high temperature (HPHT) large-volume synthesis allowed obtaining a number of novel materials [1] for new challenging applications as superhard [2,3,4,5,6], advanced electronic [7], photovoltaic [8] and thermoelectric [9, 10] materials, as well as superconductors [11, 12]: (i) boron allotropes [13, 14] (orthorhombic γ-B28 [15,16,17], pseudo-cubic t′-B52 [18]) and boron-rich compounds (boron subnitride B13N2 [19, 20]), (ii) superhard compounds with diamond structure (nanostructured cBN [21], non-stoichiometric c-BC5 [22, 23]); (iii) covalent clathrates of new stoichiometries (Na4−xSi24 [8, 9] and Na24+xSi136 [9, 10]) and even (iv) new unexpected semiconductors, like antifluorite Mg2C [24], dense Mg2C3 [25] and pure silicon allotrope with quasi-direct bandgap, Si24 [8]. A part of the lacking data can be replaced by fitted parameters of common models [26,27,28] or with ab initio calculations [29], the reliable p-V-T equations of state (EOS) data are crucial for that. In the present paper we describe the method of construction of such equations of state using integrated form of the Anderson-Gruneisen equation [30, 31]. The method is efficient even in the case of small number of experimental data [32] and may be combined with ab initio, semiempirical and even empirical modeling.

Theoretical background

EOS data and discussion

Conclusion