Method of phase transition, method for producing lead niobate-based complex oxide utilizing said phase transition method, and lead niobate-based complex oxide produced by said method

A method for producing a lead niobate-based complex oxide with an elevated proportion of pervoskite phase and lead niobate-based complex oxide produced by such method enables manufacture of small actuator or capacitor with an elevated dielectric constant k. Treatment of a raw material represented by a general formula Pb(A1/3Nb#)x(ZN1/3Nb2/3) yO3 or Pb(Fe1/2Nb1/2)x(Zn1/3Nb2/3) yO3 (wherein A is Mg or Ni; x is an atomic ratio in a range of 0-1; and y is an atomic ratio in a range of 1-0, with a relation x+y=1) and containing pyrochlore phase, under a high temperature of 500 DEG -1300 DEG C. and a high pressure of 1000-4000 kg/cm2, causes transition of pyrochlore phase into perovskite phase, thereby increasing the proportion of perovskite phase. Also treatment of a raw material represented by a general formula uPb(1/3Nb2/3)O3-vPbTiO3 (wherein u is an atomic ratio in a range of 0.5-1; and v is an atomic ratio in a range of 0.5- 0, with a relation u+v=1) and containing pyrochlore phase, under a high temperature of 500 DEG -1300 DEG C. and a high pressure of 1000-4000 kg/cm2 causes transition of pyrochlore phase into perovskite phase, thereby increasing the proportion of pervoskite phase.