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

Solid solution series of the (1-x)Pb(Lu1/2Nb1/2)O-3-x PbTiO3 binary system ceramics (PLuNT) were synthesized and hot-pressed (temperature 950 degrees C to 1130 degrees 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 similar to 258 degrees 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 less than or equal to x less than or equal to 0.38 interval within which the monoclinic angle beta proceeds a minimum near to 90 degrees at x congruent to 0.2. The morphotropic region covers the interval x = 0.38-0.49, the concentration ratio psd-M:T congruent to 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) greater than or equal to 0.02, beta greater than or equal to 90.37 degrees, 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 less than or equal to x less than or equal to 0.3. The highest electromechanical coupling coefficients: k(p) = 0.66, k(t) = 0.48, k(31) = 0.34 of (1-x) PLuN-xPT ceramics are attained in compositions near the MPB at x approximate to 0.41. Non-isovalent doping of PLuNT with La3+ in Pb sublattice shifts the MPB to lower values of x.