Formation Mechanisms of Perovskite Pb(Ni_1/3Nb_2/3)O₃ in Reaction-sintering Process

Abstract

Formation mechanisms of perovskite Pb(Ni 1/3 Nb 2/3 )O 3 (PNN) in the reaction-sintering process were investigated. Only the reflections of raw materials were detected at 400 o C. For pellets heated to 500 o C, pyrochlore phase Pb 2 Nb 2 O 7 (P 2 N 2 ) are found. Cubic Pb 3 Nb 4 O 13 (P 3 N 4 ) pyrochlore phase formed and became the main phase in pellets heated to 600 o C. After being heated to 800 o C, Pb 3 Nb 2 O 8 (P 3 N 2 ) pyrochlore phase formed in the pellets. As the pellets were heated to 900 o C, the peak of NiNb 2 O 6 columbite phase appeared. In pellets heated to 950 o C, the weak peaks of PNN perovskite phase appeared. This means the perovskite phase formed at a temperature between 900 o C and 950 o C. As the pellets were heated to 1000 o C, a large amount of PNN was formed and became dominant. The PbO, NiNb 2 O 6 and Pb 3 Nb 2 O 8 phases disappeared. The P 3 N 4 content increased with temperature in pellets heated to 1050-1200 o C. For pellets heated to 1250 o C, the P 3 N 4 content decreased significantly.

Realization of device quality PMN–PT ceramics using modulated heating method

“…Chen et al [21] have reported that the pyrochlore phase formed at 580 1C corresponds to the cubic pyrochlore Pb 3 Nb 4 O 13 . Liou et al [15] also reported the formation of cubic pyrochlore at 600 1C. The present analysis revealed a gradual change from 600 1C to 1000 1C, indicating that perovskite phase formation takes place throughout this temperature range and it is completed at around 1000 1C [16].…”

“…The pyrochlore phase is very stable and if present with the perovskite phase, it affects the quality of PMN-PT [13]. Liou et al [14] reported that the cubic Pb 3 Nb 4 O 13 (P 3 N 4 ) pyrochlore phase appeared at 600 1C, whereas the perovskite phase was formed between 900 1C and 950 1C [15]. The fact that the bonding strength of oxygen and cations in the pyrochlore is stronger than that in the perovskite, and its formation temperature (450-600 1C) is much below that of perovskite (850-1050 1C) [16], imposed the major hindrance in the synthesis of PMN-PT [17].…”