Synthesis and dielectric characterization of Pb-K-niobate SAW-single crystal

Lead-potassium-niobate, Pb2KNb5O15 (PKN) is a member of the tungsten-bronze family of the type A6B10O30, where A represents Ba, Pb, Sr, Ca, Na, K, etc.; and B represents Nb or Ta. It is a leading SAW-substrate material; at high frequencies its performance is superior to both α - quartz and lithium-niobate, LiNbO3. The synthesis of a device quality, large single crystals of this material has been a serious problem. This paper deals with the top seeded solution growth method to synthesize high quality single crystals of PKN with uniform stoichiometry and without cracks. The characterization of PKN crystals has been done by studying the temperature dependence of the dielectric constant and electrical conductivity between room temperature and 500°C. The real part of dielectric constant shows an anomaly at 468°C. However, two anomalies are found in the temperature dependence of the electrical conductivity - one at the ferroelectric Curie point at 476°C and the other at 496°C which is believed to be the ferroelastic transition point of this material. X-ray diffraction analysis indicates that PKN belonns to the c - centered orthorhombic class with the following values for lattice constants: a = 17.723Å, b = 17.987Å and c - 3.895Å.