Structure and properties of hot-pressed Pb(Lu1/2Nb1/2)O3-PbTiO3 binary system ceramics

Solid solution series of the (1 - x)Pb(Lu^sub 1/2^Nb^sub 1/2^)O^sub 3^ - x PbTiO^sub 3^ 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: k^sub p^ = 0.66, k^sub t^ = 0.48, k^sub 31^ = 0.34 of (1 - x) PLuN-xPT ceramics are attained in compositions near the MPB at x [asymptotically =] 0.41. Non-isovalent doping of PLuNT with La^sup 3+^ in Pb sublattice shifts the MPB to lower values of x.[PUBLICATION ABSTRACT]