Octahedral tilting, monoclinic phase and the phase diagram of PZT

Abstract

Abstract. Anelastic and dielectric spectroscopy measurements on PbZr 1−x Ti x O 3 (PZT) close to the morphotropic (MPB) and antiferroelectric boundaries provide new insight in some controversial aspects of its phase diagram. No evidence is found of a border separating monoclinic (M) from rhombohedral (R) phases, in agreement with recent structural studies supporting a coexistence of the two phases over a broad composition range x < 0.5, with the fraction of M increasing toward the MPB. It is also discussed why the observed maximum of elastic compliance appears to be due to a rotational instability of the polarisation and therefore cannot be explained by extrinsic softening from finely twinned R phase alone, but indicates the presence also of M phase, not necessarily homogeneous.A new diffuse transition is found within the ferroelectric phase near x ∼ 0.1, at a temperature T IT higher than the well established boundary T T to the phase with tilted octahedra. It is proposed that around T IT the octahedra start rotating in a disordered manner and finally become ordered below T T . In this interpretation, the onset temperature for octahedral tilting monotonically increases up to the antiferroelectric transition of PbZrO 3 , and the depression of T T (x) below x = 0.18 would be a consequence of the partial relieve of the mismatch between the cation radii with the initial stage of tilting below T IT .2

Elastic and anelastic relaxation behaviour of perovskite multiferroics I: PbZr0.53Ti0.47O3 (PZT)–PbFe0.5Nb0.5O3 (PFN)

“…9 [PFN] 0.1 is shown as tetragonal, based on the reported diffraction pattern [67]. Other boundaries in PT-PZ from Jaffe [38], Cordero et al [49], PZ-PFN from Lovkova et al [41] and Blazhievskii et al [40]. Red crosses mark nominal compositions of samples used in the present study, along the join Pb(Zr 0.…”

“…This phase boundary extrapolates to the location of the MPB at *160 K, *50 % PT [38,44,49], though extrapolation to *0 K at *50 % PT has also been shown in some phase diagrams [50,51]. Diffraction and dielectric evidence for a tilting transition at *210 K in Pb(Zr 0.52 Ti 0.48 )O 3 [52,53] is consistent with the topology given by Cordero et al [44] and calculated from first principles by Kornev et al [54].…”

“…There is a rounded minimum in the Young's and shear moduli at temperatures corresponding to the expected location of the tetragonal-monoclinic transition in PZT [49,[105][106][107][108][109]112]. The transition appears to be reversible for Pb ( [106,109].…”

“…The transition appears to be reversible for Pb ( [106,109]. If there is any associated anomaly in Q À1 , it is perhaps only a slight increase with falling temperature through the transition at both Hz and kHz frequencies [49,[105][106][107]109]. By way of contrast, a poled sample of Pb(Zr 0.52 Ti 0.48 )O 3 displayed a sharp minimum in the Young's modulus measured at *150 kHz [52,60,113,114].…”

“…There are as yet no data for strain relaxation effects in PZT-PFN multiferroics, but lattice parameters and elasticity data from the literature for Pb ( Changes in elastic properties have been studied extensively for PZT [44,49,[105][106][107][108][109]. As expected for improper ferroelastic cubic-tetragonal and cubicrhombohedral transitions with strong coupling between symmetry breaking shear strains and the order parameter, measurements at Hz and kHz frequencies on ceramic samples with compositions close to the MPB show large (*50 %) softening of the Young's modulus, 1/S 11 , and shear modulus, G [44,[105][106][107]109].…”