Effect of La2O3 Modified on Pyroelectric Properties of 0.69Pb(Mg1/3Nb2/3)O3-0.31PbTiO3 Solid Solutions

The pyroelectric and polarization properties of La2O3 modified 0.69Pb(Mg1/3Nb2/3)O-3-0.31PbTiO(3) solid solution systems were examined by the static technique as a function of temperature. The peak temperature of the pyroelectric coefficient maxima was decreased by La2O3. From the pyroelectric data, two major anomalies corresponding to the rhombohedral -> tetragonal -> cubic phase transitions were observed. This suggests that the successive transition of 0.69Pb(Mg1/3Nb2/3)O-3-0.31PbTiO(3) systems appeared not to be affected by La2O3. The optimum conditions for obtaining compositions with improved pyroelectric properties (p similar or equal to 0.013 C/m(2)K at 126 degrees C, P-s similar or equal to 0.197 C/m(2) at 25 degrees C) are a sintering temperature of 1250 degrees C and the nominal addition of 0.03 wt. % La2O3. The figures of merit (F-v similar or equal to 0.034 m(2)/C, F-d similar or equal to 0.357 x 10(-4) Pa-1/2) of the composition 0.69Pb(Mg1/3Nb2/3)O-3-0.31PbTiO(3)-0.03 wt. % La2O3 are comparable to that of TGS and LiTaO3. Also, the piezoelectric constant (d(33)) and the electromechanical coupling factor (k(p)) were found to be about 379 - 422 x 10(-12) C/N and 0.274 - 0.342 for 0.69PMN-0.31PT-xLa systems, respectively.