DIELECTRIC AND OPTICAL STUDIES OF THE LOW-TEMPERATURE PHASE IN NANBO3 - EFFECT OF MANGANESE DOPANT

Pure and Mn-doped NaNbO3 crystals have been investigated dielectrically between 380 and 20 K. Below room temperature, no phase transition is observed in pure sodium niobate. With increasing Mn content, a structural phase transition is induced around 140 K. The dielectric constant shows a maximum for the sample with 0.7 wt.%, and shows large thermal hysteresis. In the low-temperature region, ferroelectric activities could not be detected in either pure or lightly doped NaNbO3. The phase diagram of T(c) vs the concentration of Mn is obtained. Domain motion associated with this phase transition is observed around the transition temperature. This evidence proved that the low-temperature phase is induced by light doping with Mn ions. The uniaxial stress decreases T(c); dT(c)/dsigma = -80 K/kbar on heating and -600 K/kbar on cooling.