The effect of second phase La0.67TiO2.87 on the phase structure and impedance spectroscopy of La2Ti2(1 + x)O7 piezoelectric ceramics

Abstract The Ti excess La 2 Ti 2 (1+ x ) O 7 ( x  = 0, 0.005, 0.01, 0.02, 0.05, 0.1) piezoelectric ceramics have been prepared by sol-gel technology and solid state synthesis method. Through refinement analysis, the phase structure of the ceramics varies with Ti content. Most monoclinic phase (∼93%) and a handful of orthogonal phase (∼7%) coexist in La 2 Ti 2 (1+0) O 7 ceramics. Pure monoclinic phase La 2 Ti 2 O 7 with space group P2 1 appears in La 2 Ti 2 (1+0.005) O 7 and La 2 Ti 2 (1+0.01) O 7 ceramics. Monoclinic phase La 2 Ti 2 O 7 and a certain proportion of tetragonal phase La 0.67 TiO 2.87 coexist in La 2 Ti 2 (1+0.02) O 7 , La 2 Ti 2 (1+0.05) O 7 and Ti 2 (1+0.1) O 7 ceramics. With the excess of Ti content, the monoclinic phase ratio and distortion angles in a-b projection plane of the ceramics increase first and then decrease, which is consistent with the variation tendency of piezoelectric constant d 33 . The excellent piezoelectric constant for Ti 2 (1+0.01) O 7 ceramics is 2.8 pC/N. Impedance analysis shows that the conductive mechanisms of all samples include both grain and grain boundary conductivity at temperature range T  ≥ 500 °C. The formation of tetragonal phase La 0.67 TiO 2.87 derives from Ti excess in pure monoclinic phase La 2 Ti 2 O 7 . The existence of tetragonal phase La 0.67 TiO 2.87 can obviously increase the capacitance of ceramics at x  ≥ 0.05. All prepared piezoelectric La 2 Ti 2 (1+ x ) O 7 ceramics have highly frequency stability and are candidates for ultrahigh temperature piezoelectric application.