The effect of pyrochlore phase on formation mechanism and electrical properties of perovskite PZMN relaxors

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

“…5). 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.…”

“…Hence, a minimum heating rate of 10 1C/min or even higher for calcination in the temperature range upto 600 1C was found to be efficient in preventing pyrochlore phase formation. Subsequent slow heating rate of 2 1C/min from 600 1C to 850 1C may enhance the P 3 N 2 pyrochlore phase formation which is an excellent precursor for perovskite PMN-PT [18,21]. After the phase stabilization, it was observed that the alumina dish in which the stoichiometric sample was calcined did not show any colouration, where as the case of samples with excess PbO, the dish had orange coloration indicating the PbO vaporization [27].…”

“…This is to minimize PbO evaporation which leads to the formation of pyrochlore phase. Three possible pyrochlore phases, reported in the synthesis of PMN-PT are: i) stoichiometric rhombohedral pyrochlore Pb 2 Nb 2 O 7 (P 2 N 2 ), ii) B-site deficient Pb rich tetragonal pyrochlore Pb 3 Nb 2 O 8 (P 3 N 2 ) and iii) A-site (Pb) deficient cubic pyrochlore Pb 3 Nb 4 O 13 (P 3 N 4 ) [13,21]. Of the possible reasons for the pyrochlore phase formation, the most prominent is the lead loss during calcination and sintering which results in the formation of Pb-deficient cubic pyrochlore.…”

“…The requirement of pure columbite-like phase was also stressed upon in other studies [18]. Although several earlier studies on the synthesis of PMN-PT used excess PbO [21,25,26] to minimize the percentage of pyrochlore formation, the exact amount of excess PbO required has not been reported. While it was presumed that excess PbO would have evaporated at around the calcination temperature $ 850 1C, no attempts have been reported to remove the unreacted PbO, if at all left in the sample.…”

Phase evolution, dielectric and impedance spectroscopic study of SrNb2O6 columbite phase

“…These niobates also have very important role in the synthesis of perovskite with general formula A 0 (B 0 1/3 B 00 2/ 3 )O 3 type materials (where A 0 = Pb 2+ , Ba 2+ or Sr 2+ ; B 0 = Mg 2+ , Zn 2+ , Ni 2+ , Co 2+ , or Mn 2+ and B 00 = Nb 5+ ) [6][7][8][9][10][11][12][13][14]. In the present investigation, efforts were made to prepare SrNb 2 O 6 ceramics using simple solid-state reaction route.…”