Thermal expansion and compressibility of Ca3Al4ZnO10 – an unusual tetrahedral framework structure

Abstract

Melt-grown single crystals of Ca3Al4ZnO10 have been structurally characterized at ambient conditions (space group Pbcm, a = 5.1364(3), b = 16.7403(9), c = 10.7019(6) Å, V = 920.20(8) Å3, Z = 4, R(|F|) = 0.026 for 1116 reflections with I > 2σ(I) and 95 parameters). Our results show that the compound had been previously described in unnecessarily low symmetry. It represents a three-dimensional network of corner-sharing [(Al,Zn)O4]-tetrahedra containing oxygen atoms simultaneously linking three adjacent tetrahedra. Charge compensation is provided by Ca ions residing in voids of the network. The high-temperature and high-pressure behavior was elucidated between 25(2) and 797(2) °C and between ambient pressure and 6.8(1) GPa. No indications for structural phase transitions have been found. However, a diffraction experiment performed at 9.0(1) GPa gave evidence for the beginning of an amorphization. From the evolution of the lattice parameters thermal expansion and compressibility tensors have been obtained. The behavior of Ca3Al4ZnO10 at non-ambient conditions conforms with the so-called inverse relationship for temperature and pressure, i.e. isobaric thermal expansion and isothermal compression have opposite effects on changes of structural parameters.