Anisotropic thermal expansion of monoclinic potassium lutetium tungstate single crystals

The anisotropic thermal expansion of a single crystal of KLu(WO4)2(KLuW), obtained by the top-seeded solution growth method, has been investigated over a wide temperature range (50–600 °C). The linear thermal-expansion tensor has been determined and its principal X, Y, and Z axes are in the [705], [010], and [107] crystallographic directions, respectively. The principal thermal-expansion coefficients αI, αII, and αIII are 12.8×10−6, 7.8×10−6, and 22.2×10−6K−1, respectively. The principal axis with maximum thermal expansion (Z with αIII=22.2×10−6) is located at 10.37° from the c axis. In comparison with KGd(WO4)2 and KYb(WO4)2, the thermal-expansion anisotropy of KLuW is weaker and therefore optical-quality crystals are easier to obtain than with KGdW and KYbW from a thermal-expansion standpoint.