Microscopic analysis of the compressibility in the spinel phase of

Departamento de Química Física y Analítica, Facultad de Química Universidad de Oviedo - E-33006-Oviedo, Spain

Received: 8 November 2000
Accepted: 2 April 2001

Abstract

Quantum-mechanical static simulations of the high-pressure spinel phase of have been performed to determine the unit cell geometry and the equation of state from 0 to 50 GPa. The application of the Bader theory to the ab initio electron density leads to quantum consistent atomic charges and volumes, the crystalline bonding graph, and the prediction of a highly ionic bonding. The computed thermodynamic properties have been interpreted in terms of the local behaviour of the and quantum subgroups and constitutive unit cell polyhedra. We show that: i) the bulk compressibility can be estimated from the average of the tetrahedral and octahedral compressibilities, and ii) the response to pressure controls the macroscopic behaviour. Our conclusions can be useful in the search of very hard, -based materials.