Structure and properties of hot-pressed Pb(Lu1/2Nb1/2)O-3-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 piezoe lectric properties were studied. Pure lutecium niobate PLuN (x = 0) has a p ronounced long-range order in the B-sublattice and an antiferroelectric to paraelectric phase transition at similar to 258 degrees C. The phase struct ure of the PLuNT system, at room temperature, changes from a pseudomonoclin ic (psd-M, space group Bmm2) to tetragonal (T, space group P4mm). The pseud omonoclinic phase extends over the 0 less than or equal to x less than or e qual to 0.38 interval within which the monoclinic angle beta proceeds a min imum near to 90 degrees at x congruent to 0.2. The morphotropic region cove rs 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 th e 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 dispersi on and broadening of the phase transition, features typical to relaxors, ar e 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 coeffici ents: 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-isoval ent doping of PLuNT with La3+ in Pb sublattice shifts the MPB to lower valu es of x.