Correlation of polar order in K_1-xNa_xTaO₃

Second-harmonic light generation and birefringence data are reported for KTaO3. They are evaluated in terms of an inhomogeneous lattice polarization. The correlation of polar orientation is shown to extend to hundreds of Å in the paraelectric phase of KTaO3. A sharp increase of the correlation length for 15% Na doping to 1500 Å is associated to the polar transition at 12 K. From the low-temperature value of the correlation length, conclusions are drawn about the nature of the polar phase. © 1989, IOP Publishing Ltd.