Structure-Property Relationships in Entropy-Stabilized Oxides I. Thermal Properties

Abstract

Materials science is challenged with developing new materials in order to meet the demands of technological innovation. Consequently, this opens the door to novel or complex properties awaiting exploration. Entropy-stabilized oxides (ESOs) demonstrate the viability of materials engineering using configurational entropy to drive phase stabilization. The prototype ESO MgxNixCoxCuxZnxO, x=0.2, (J14), exhibits a rocksalt structure where cations are distributed randomly on one FCC sublattice with minimal positional disorder, and an interleaved FCC anion sublattice with oxygen ions displaced to accommodate the distortions in the cation polyhedra. Using time domain thermoreflectance (TDTR), we measure thermal conductivity of J14 for comparison with other, less disordered compositions containing the same constituents and more disordered 6-component systems (J14+X, where X = Cr, Ge, Sc, Sn, or Sb). Thermal conductivity systematically decreases with increasing configurational disorder, approaching the minimum limit, which is typically reserved for amorphous phases. Results are discussed in terms of various scattering mechanisms including mass, strain, and volume effects, emphasizing understanding of thermal properties from a local structural perspective. In this talk we focus on the experimental process of elimination using several metrology techniques in conjunction with TDTR to gain meaningful perspective on configurationally disordered, highly crystalline systems.