STRUCTURE AND NONLINEAR-OPTICAL PROPERTIES OF KTIOASO4

Refinements of the crystal structures of potassium titanyl arsenate, K TiOAsO4, grown from a tungstate flux (1) and an arsenate flux (2), are reported. Crystal data at room temperature are: (1) KTiOAsO4, orthorh ombic, Pna2(1), a = 13.138 (2), b = 6.582 (1), c = 10.787 (2) Angstrom , Z = 8, R = 0.027 for 2086 reflections with I > 3 sigma(1); (2) KTiOA sO4, orthorhombic, Pna2(1), a = 13.130 (2), b = 6.581 (1), c = 10.781 (1) Angstrom, Z = 8, R = 0.020 for 2716 observed reflections with I > 3 sigma(1). The values of the linear and non-linear optical susceptibi lities for KTiOAsO4 are discussed using the isostructural non-linear o ptical crystal KTiOPO4 as a starting point. The observed increase in c ertain nonlinear optical coefficients of KTiOAsO4 is shown to derive p rincipally from the increase in the linear refractive indices brought about by the substitution of phosphorus by arsenic in the structure.