Structure and Properties of Hot-Pressed Pb(Lu1/2Nb1/2)O3-PbTiO3 Binary System Ceramics*

Abstract

Solid solution series of the (1 - x)Pb(Lu1/2Nb1/2)O3 - x PbTiO3 binary system ceramics (PLuNT) were synthesized and hot-pressed (temperature 950°C to 1130°C, pressure 25 MPa); its structure, dielectric and piezoelectric properties were studied. Pure lutecium niobate PLuN (x = 0) has a pronounced long-range order in the B-sublattice and an antiferroelectric to paraelectric phase transition at ∼258°C. The phase structure of the PLuNT system, at room temperature, changes from a pseudomonoclinic (psd-M, space group Bmm2) to tetragonal (T, space group P4mm). The pseudomonoclinic phase extends over the 0 ≤ x ≤ 0.38 interval within which the monoclinic angle β proceeds a minimum near to 90° at x ≅ 0.2. The morphotropic region covers the interval x = 0.38 - 0.49, the concentration ratio psd-M:T≅ 1 (the morphotropic phase boundary—MPB) corresponds to x = 0.41. Within the morphotropic region, a rather strong distortion of the unit cell—(c/a - 1)≥ 0.02, β ≥ 90.37o, characteristic of “hard” piezoelectrics is maintained. Dielectric dispersion and broadening of the phase transition, features typical to relaxors, are observed within the concentration interval of 0.1 ≤ x ≤ 0.3. The highest electromechanical coupling coefficients: kp = 0.66, kt = 0.48, k31 = 0.34 of (1 - x) PLuN−xPT ceramics are attained in compositions near the MPB at x ≈ 0.41. Non-isovalent doping of PLuNT with La3+ in Pb sublattice shifts the MPB to lower values of x.