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 +/- 0.4 GPa to 11.8 +/- 0.5 GPa and a reduced elastic modulus of 162 +/- 5 GPa up to 178 +/- 6 GPa. Furthermore, the optical properties of the spinel-type materials were studied by spectroscopic ellipsometry in the wavelength range of 250-1000 nm. All materials exhibit a high refractive index ranging from n = 2.20 to n = 2.10 at 430.8 nm (Fraunhofer G line) with a similar low dispersion (0.09 to 0.07). (C) 2017 Elsevier Ltd. All rights reserved.