Growth, structural and thermophysical properties of TbNbO4 crystals

Abstract

A new TbNbO₄ single-crystal with a monoclinic structure has been grown successfully using the Czochralski method for the first time. The material belongs to the space group C2/c, with unit-cell parameters of a = 7.173(3) Å, b = 11.186(5) Å, c = 5.156(2) Å and β = 131.082(3)°. The thermal properties of the as-grown TbNbO₄ crystal, including specific heat, thermal expansion coefficient, thermal diffusion coefficient, and thermal conductivity, were measured systematically. The TbNbO₄ crystal exhibits strong anisotropic thermal expansion; a negative thermal expansion along the c direction is presented, and a zero thermal expansion coefficient in some directions can be obtained. The emission and absorption spectra were also measured. The strongest emission peak in the green spectral domain of TbNbO₄ corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺ is located at 549 nm. In the range of 350–1500 nm, the as-grown TbNbO₄ crystal has low absorption. X-ray photoelectron spectroscopy (XPS) was used to study the valence of the elements in the TbNbO₄ crystal; the result shows that there are two different valence states of Tb in the as-grown crystal.