Thermal expansion, mechanical and optical properties of gallium and aluminum substituted Zn2TiO4 spinels

Polycrystalline samples of new Zn1.75Ti0.75Ga0.5O4, Zn1.5GaTi0.5O4, and Zn1.75Ti0.75Al0.5O4 spinel were prepared by solid-state reactions. Phase analysis and structural investigations were carried out by powder X-ray diffraction and Raman spectroscopy. In situ high-temperature powder X-ray diffraction experiments enabled the investigation of the thermal expansion of the spinel-type compounds. To determine the mechanical properties, nanoindentation experiments were performed with a Berkovich diamond indenter tip. Analyses of the load–displacement curves revealed a high hardness ranging from 10.2±0.4GPa to 11.8±0.5GPa and a reduced elastic modulus of 162±5GPa up to 178±6GPa. Furthermore, the optical properties of the spinel-type materials were studied by spectroscopic ellipsometry in the wavelength range of 250–1000nm. All materials exhibit a high refractive index ranging from n=2.20 to n=2.10 at 430.8nm (Fraunhofer G line) with a similar low dispersion (0.09 to 0.07).