Structural redetermination, thermal expansion and refractive indices of KLu(WO₄)₂

Abstract

The crystal structure of monoclinic KLu(WO 4 ) 2 (KLuW) crystals was determined at room temperature by using single-crystal X-ray diffraction data. The unit-cell parameters were a = 10.576 (7), b = 10.214 (7), c = 7.487 (2) Å, β = 130.68 (4)°, with Z = 4, in space group C 2/ c . The unit-cell parameters of KLu 1− x Yb x (WO 4 ) 2 were determined in relation to Yb concentration. Vickers micro-indentations were used to study the microhardness of KLuW. The linear thermal expansion tensor was determined and the principal axis with maximum thermal expansion (\alpha_{33}' = 16.72 × 10 −6 K −1 ), X_3', was located 13.51° from the c axis. The room-temperature optical tensor was studied in the near-infrared (NIR) and visible range. The principal optical axis with maximum refractive index ( n g = 2.113), N g , was located 18.5° from the c axis at 632.8 nm. Undoped and ytterbium-doped KLuW crystals were grown by the TSSG (top-seeded-solution growth) slow-cooling method. The crystals show {110}, {\bar{1}11}, {010} and {310} faces that basically constitue the habit of the KLuW crystals.