PHYSICAL-PROPERTIES OF SINGLE-CRYSTALS OF KTIPO4, KXRB1-XTIOPO4 (X=0.85-0.75), KGEOPO4 AND KTIOASO4

Single crystals of the title compounds of optical quality and dimensions up to 30 x 25 x 25 mm were grown by the flux method. During the growth process the formation of twins consisting of bicrystals was observed, even in the case of single-crystalline seeds. The twinning boundaries could be detected by etching with hot KOH solutions. The following physical properties were investigated: refractive indices, dielectric constants, thermal expansion, piezoelectric, and electrooptic effects, elastic and thermoelastic constants. The crystals exhibit a quite similar behaviour. The anisotropy of all properties is quasi-tetragonal. In respect to polar properties only small differences within the mixed crystals KxRb1-xTiOPO4 are found. Replacement of P by As does only slightly affect the polar properties, whereas the replacement of Ti by Ge leads to a drastic reduction of polar effects.