OBSERVATION OF A NEAR-STATIC CONDENSATION OF POLARIZATION FLUCTUATIONS IN STRONTIUM BARIUM NIOBATE

The dielectric response characteristics of SrxBa 1-xNb2O6 for 0.50<x<0.75 have been investigated as a function of temperature. Cold-stage transmission electron microscopy studies were performed for comparative purposes. An anomalous relaxation of tan δ was observed in the temperature range of -100 to -50°C, which was previously unreported. Near this temperature range the dielectric constant was also found to become frequency independent. These results are interpreted in terms of a near-static condensation of polarization fluctuations, reflecting the trailing edge of the relaxation time distribution approaching long time periods. Selected-area electron-diffraction investigations revealed an incommensurate reflection along the 〈110〉 which exhibits diffuse scattering. Near the temperature of the static condensation of polarization fluctuations, the degree of diffuse scattering was found to decrease significantly. In addition, bright-field imaging revealed a significant increase in the size of needlelike nanosized ferroelectric regions in this temperature range. It is proposed that the near-static condensation of polarization fluctuations is driven by small structural changes in the channels of the tungsten bronze structure. © 1995 American Institute of Physics.