Structure and properties of novel Pb(B′1/2Nb1/2)O3-PbTiO3 binary systems with high piezoelectric coupling

The (1-x)Pb(Lu1/2Nb1/2)O-3-XPbTiO3 (PLuNT) and (1-x)Pb(Er1/2Nb1/2)O-3-xPbTiO(3) (PErNT) binary systems have been originally synthesized. 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 degreesC. 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 to0.2. The morphotropic region covers over the interval x = 0.38-0.49, the concentration ratio psd-M:T congruent to1 (the morphotropic phase boundary MPB) corresponds to x = 0.41. 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 to0.41. Non-isovalent doping of PLuNT with La3+ in Pb sublattice shifts the MPB to lower values of x. The unit cell of erbium niobate (PErN) is described as pseudomonoclinic of orthorhombic Bmm2 symmetry: a=c=4.2161 Angstrom; b=4.0869 Angstrom; beta =90.55 degrees and composition is characterized with antiferroelectric phase transition at 305 degreesC. The PErNT system has the morphotropic phase region extending over the x=0.4-0.6 interval.