Heat Capacities of Nanostructured Wurtzite and Rock Salt ZnO: Challenges of ZnO Nano-Phase Diagram

Abstract

Low-temperature heat capacities (Cp) of nanostructured rock salt (rs-ZnO) and wurtzite (w-ZnO) polymorphs of zinc oxide were measured in the 2–315 K temperature range. No significant influence of nanostructuring on Cp of w-ZnO has been observed. The measured Cp of rock salt ZnO is lower than that of wurtzite ZnO below 100 K and is higher above this temperature. Using available thermodynamic data, we established that the equilibrium pressure between nanocrystalline w-ZnO and rs-ZnO is close to 4.6 GPa at 300 K (half as much as the onset pressure of direct phase transformation) and slightly changes with temperature up to 1000 K.

ZnO under Pressure: From Nanoparticles to Single Crystals

“…The synthesis of rs-ZnO nanocrystalline bulks in large-volume high-pressure apparatuses [17] made it possible to experimentally study its properties at ambient pressure [75][76][77]. Low-temperature heat capacities (C p ) of rs-ZnO and w-ZnO nanobulks were measured in the 2-315 K temperature range [75]. No significant influence of nanostructuring on C p of w-ZnO was observed.…”

Lattice thermal conductivity of ZnO: experimental and theoretical studies

“…22 Kemenev et al measured the low-temperature heat capacity (5-290 K) of both wurtzite and rock salt phases of ZnO and reported a lower value of k around 256 K and 226 K, respectively. 23 Temperature-dependent PL spectroscopy can also predict y D by fitting the Varnish Equation. The Debye temperature can be measured using various other means like using elastic constants (477 K) 24 and neutron scattering (963 K).…”