Formation and sintering of La 2Zr 2O 7 by the hydrazine method

Abstract

In the ZrO 2La 2O 3 system, metastable c-ZrO 2 solid solutions ( ss) containing up to ≈ 27 mol% La 2O 3 crystallize at low temperatures from amorphous materials prepared by the hydrazine method. The lattice parameter a increases linearly from 0.5152 to 0.5350 nm. The formation of pyrochlore La 2Zr 2O 7 proceeds via two reaction processes: (1) decomposition of c-ZrO 2( ss) ( c-ZrO 2( ss)→La 2Zr 2O 7 + t-ZrO 2) and (2) solid-state reaction of t-ZrO 2 and La 2O 3. Dense La 2Zr 2O 7 ceramics (99.5% of theoretical) with an average grain size of 10 μm have been fabricated by hot isostatic pressing for 2 h at 1500°C and 196 MPa. Their fracture toughness and bending strength are 1.9 MPa m 1 2 and 172 MPa, respectively. They exhibit a high electrical conductivity of 1.5 × 10 −1 S m −1 at 1000°C.