Growth, structural, thermal, and optical properties of a GaNbO4 single crystal

A GaNbO4 single crystal (phi = 24 mm) was successfully grown for the first time by the Czochralski (CZ) method, and the thermal and optical properties were systematically studied. The structure parameters were calculated and belong to the monoclinic C2/m space group. The half-peak width of the rocking curve is 26.63 arcsec, indicating that the crystal is of relatively high quality. The specific heat, thermal diffusion coefficient, and thermal conductivity were measured systematically. The thermal expansion coefficients of the GaNbO4 crystal in different directions were obtained and it is proved that the GaNbO4 crystal has negative thermal expansion along the crystallographic b-axis. The orientation relationship between the thermal expansion ellipsoid axis and the crystallographic axis is determined. The UV-vis diffuse reflectance spectra and the transmittance spectra of the GaNbO4 crystal were measured, and the band gap and the orientation relationship between the optical axis and crystallographic axis were confirmed. The chemical composition was analyzed using X-ray photoelectron spectroscopy (XPS).