Electric quadrupole interaction in sodium niobate

To investigate the effect of phase transitions in ferroelectrics upon parameters of quadrupole bond, studied was the electric quadrupole interaction in sodium niobate. The experiment was conducted on NaNbO3 ceramic containing up to 1% of hafnium impurity. The method of perturbed angular γ-γ correlations from a 181Ta source has been used. Parameters of quadrupole bond were measured for rhombic anti-ferroelectric and pseudotetragonal nonpolar crystalline modifications at 340 and 390 deg C, respectively. It has been revealed that the phase transition is not accompanied by a substantial change of the bond character. Conclusions are made that the frequency of quadrupole precession is determined mainly by the degree of cubic structure distortion; the frequency of quadrupole precession decreases with increasing temperature; the value of the frequency spreading parameter for a given crystal turns out to be a substantially small value