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The transition from the rhombohedral-ferroelectric to the lower temperature orthorhombic-antiferroelectric phase in Zr-rich PZT involves two order parameters (OPs): 1) the polar OP for the displacements of the cations with respect to the O octahedra; 2) an antiferrodistortive OP responsible for tilting of the octahedra. It is shown that at Ti compositions near the morphotropic boundary with the FE phase (0.046 ≤ x ≤ 0.054), the two OPs may be almost independent of each other at cooling rates of 0.5 K/min or faster, depending on the sample history. This fact gives rise to a great variety of shapes of the curves of the elastic compliance s(T), but all of them can be fitted very well as superpositions of variously broadened steps for each of the modes involved in the transitions, including the tilt transition occurring in the untransformed FE fraction. The evolution of the s(T) curves includes enhancements up to a factor of four during aging for weeks in the region of the AFE/FE coexistence. Restiffening and reduction of the thermal hysteresis of the AFE/FE transition are recovered by heating up to 800-900 K. It is proposed that ageing is due to the clustering of relatively mobile defects, most likely O vacancies, at the domain walls in the coexisting AFE/FE phases. Such defect structures are probably at the origin of intense thermally activated relaxation processes observed above TC in the dielectric and anelastic spectra, and can be annealed out above 800 K, allowing the AFE transition to recover a fast kinetics.

We present the results of dielectric and anelastic spectroscopy measurements, together with X-ray diffraction investigations, which allow us to establish more precisely the phase diagram of Pb1-xLax(Zr0.9Ti0.1)1-x/4O3 (PLZT x/90/10) in the compositional range around the AFE/FE phase boundary (00.032 are antiferroelectric with orthorhombic Pbam structure. In-between, for compositions with 0.025⩽x⩽0.032, a coexistence of the AFE/FE phases is evidenced. The use of complementary dielectric and anelastic techniques allows to follow the phase transitions shifts throughout all the interesting composition range and to construct the temperature-composition phase diagram. The tilt instability line, separating the R3c and R3m low and high temperature phases, has been evidenced. Moreover, the new transition, associated with the onset of disordered tilting preceding the long range order of the R3c phase, previously found in Zr-rich Pb(Zr,Ti)O3, is confirmed in rhombohedral PLZT x/90/10 compositions. [ABSTRACT FROM AUTHOR]

The transition from the rhombohedral-ferroelectric to the lower temperature orthorhombic-antiferroelectric phase in Zr-rich PZT involves two order parameters (OPs): 1) the polar OP for the displacements of the cations with respect to the O octahedra; 2) an antiferrodistortive OP responsible for tilting of the octahedra. It is shown that at Ti compositions near the morphotropic boundary with the FE phase (0.046 ≤ x ≤ 0.054), the two OPs may be almost independent of each other at cooling rates of 0.5 K/min or faster, depending on the sample history. This fact gives rise to a great variety of shapes of the curves of the elastic compliance s(T), but all of them can be fitted very well as superpositions of variously broadened steps for each of the modes involved in the transitions, including the tilt transition occurring in the untransformed FE fraction. The evolution of the s(T) curves includes enhancements up to a factor of four during aging for weeks in the region of the AFE/FE coexistence. Restiffening and reduction of the thermal hysteresis of the AFE/FE transition are recovered by heating up to 800-900 K. It is proposed that ageing is due to the clustering of relatively mobile defects, most likely O vacancies, at the domain walls in the coexisting AFE/FE phases. Such defect structures are probably at the origin of intense thermally activated relaxation processes observed above TC in the dielectric and anelastic spectra, and can be annealed out above 800 K, allowing the AFE transition to recover a fast kinetics. [ABSTRACT FROM AUTHOR]

The phase transformations of ceramic PbZri1-xTixO3 are studied at the composition x = 0.05 close to the morphotropic phase boundary between antiferroelectric orthorhombic Pbam and ferroelectric rhombohedral phases by elastic, dielectric, and x-ray diffraction measurements. Temperature scans at different rates show that the kinetics of the transition from R3m to Pbam is very sluggish, and is actually split into a slower polar component, appearing in the dielectric susceptibility and a nonpolar component, visible as a sharp stiffening of the Young's modulus. The latter is assigned to the establishment of the oxygen octahedral tilt pattern of the Pbam phase, and occurs at once at a temperature that decreases with increasing cooling rate. On heating, the transition occurs at a temperature 65 K higher than on quasistatic cooling, so that both components occur with a faster rate almost together. The Young's modulus presents a variety of apparently different types of anomalies, depending on temperature rate and history, which, however, can be well reproduced in terms of steplike anomalies corresponding to the two components of the Pbam ↔ R3m transition and the tilt R3c ↔ R3m transition in the region of coexistence of the FE and AFE phases. [ABSTRACT FROM AUTHOR]

Abstract: We present anelastic spectroscopy measurements between 2 and 500K in Ba1−x La x TiO3 (0.10≤ x ≤0.20). The phase transitions of pure BaTiO3 are shifted to lower temperature by increasing the La doping and are completely suppressed starting from x =0.15. The samples are expected to contain H impurities since sintering was performed in flowing H2 to ensure electronic rather than cation vacancy compensation, and indeed at least three relaxation processes of the complex anelastic spectrum are strongly influenced by annealing the samples in CO or H2 at 1450K. A thermally activated anelastic peak around 250K (f ∼2kHz) is ascribable to H hopping between different O atoms, while a possible indication of fast reorientation around a same O atom comes from a broad peak around 100K. At least other three relaxation processes are present between 30 and 150K, but the present data do not allow their nature to be ascertained; possible mechanisms involve polarons and hopping of Ti and possibly La among off-centre positions. [Copyright &y& Elsevier]

Abstract: A detailed study of the relaxation process occurring in polycrystalline ZrV2H x (0≤ x ≤1) below room temperature has been carried out by means of acoustic spectroscopy. At low H concentrations the main effect is due to the well known martensitic phase transformation around 120K. Moreover a H-related thermally activated peak is detected around 240K, at a vibration frequency of about 3.5kHz. The peak features and the relaxation parameters are discussed in terms of the possible kinds of H dynamic giving rise to the anelastic effect. For the highest values of x a clear effect due to H ordering is visible around 200K. In addition, a new thermally activated process is detected around 140K and the experimental data can be satisfactorily fitted with the superposition of two broad peaks with activation energies of 0.14 and 0.17eV. These processes are due to the jumps of H atoms, likely among tetrahedral interstitial sites in the lattice of the Laves phase. [Copyright &y& Elsevier]

The anelastic spectra of La1−xCaxMnO3 with x just below 0.50 have been measured in order to better characterize the nature of the phase transitions and microscopic lattice relaxation processes present in these materials. A peak in the imaginary part of the elastic susceptibility around 30 K below the Curie temperature TC presents a behaviour typical of inhomogeneous and glass-like systems. We have performed a quantitative analysis calculating the temperature dependent distribution function of the energy barriers of the fluctuations characterizing this nanostructured state. [Copyright &y& Elsevier]

We report anelastic spectroscopy measurements of La[SUB1-x]Ca[SUBx]MnO[SUB3] performed in order to better characterize the nature of the phase transitions and microscopic lattice relaxation processes present in these materials. A peak in the imaginary part of the elastic susceptibility presents a behaviour typical of inhomogeneous and glass-like systems. We have performed a quantitative analysis calculating the temperature dependent distribution function of the energy barriers of the fluctuations characterizing this nanostructured state. [ABSTRACT FROM AUTHOR]

• The anelastic and dielectric spectra of MAPbI3 and FAPbI3 clarify the nature of their structural phase transitions. • The cubic to tetragonal phase transition is mainly driven by tilting of the relatively rigid PbI6 octahedra. • The transition to the orthorhombic phase is driven by blocking of the MA/FA rotation, followed by anelastic relaxation of MA. The metal-organic halide perovskites may have excellent photovoltaic properties, useful to create cheap and efficient solar cells, photodetectors and LEDs with a wide range of colors. Great efforts are spent for improving their scarce stability and clarifying the mechanisms that allow the photocarriers to have so long lifetimes. These phenomena are closely connected to the structural transformations and to the dynamics of the reorienting organic cations, both of which can be studied by anelastic measurements, here combined with dielectric spectroscopy. The complex dynamic Young's modulus and permittivity of MAPI and FAPI have been measured on samples obtained by pressing the powders into bars or disks. Both perovskites are cubic at and above room temperature (α phase), with freely rotating FA and MA cations, and undergo two tilt transitions of the PbI 6 octahedra into a tetragonal (β) and orthorhombic (γ) phase, accompanied by losses of the orientational degrees of freedom of the MA and FA molecular cations. These α → β and β → γ transitions are accompanied respectively by sharp softening and stiffening of the Young's modulus, while the permittivity has a major drop from a paraelectric rise at the β → γ transition of MAPI and is practically flat everywhere in FAPI. From these behaviors we argue that the α ∕ β transition is mainly due to octahedral tilting while the latter to the blocking of MA/FA reorientational modes linearly coupled with strain. Comparisons are made with elastic anomalies found in other hybrid 3D and layered perovskites. [ABSTRACT FROM AUTHOR]

The traditional derivation of the elastic anomalies associated with ferroelectric (FE) phase transitions in the framework of the Landau theory is combined with the piezoelectric constitutive relations instead of being explicitly carried out with a definite expression of the FE part of the free energy. In this manner it is shown that the softening within the FE phase is of electrostrictive and hence piezoelectric origin. Such a piezoelectric softening may be canceled by the better known piezoelectric stiffening, when the piezoelectric charges formed during the vibration are accompanied by the depolarization field, as for example in Brillouin scattering experiments. It is therefore possible to evaluate the average piezoelectric coupling from the usual elastic measurements of unpoled ceramics, where the piezoelectric stiffening does not occur. As experimental validation, we present new measurements on Zr-rich lead zirconate titanate (PZT), where the FE phase transforms into antiferroelectric on cooling or doping with La, and a comparison of existing measurements made on FE PZT with low frequency and Brillouin scattering experiments. [ABSTRACT FROM AUTHOR]

The rotational instability of the electric polarization P during phase transformations between ferroelectric phases is of great practical interest, since it may be accompanied by extremely large values of the piezoelectric coefficient, and a divergence of the coupled shear compliance contributes to such enhancements. In the literature, this has been explicitly calculated in the framework of the Landau theory and discussed with specific numerical simulations involving tetragonal, orthorhombic, and rhombohedral ferroelectric phases. When monoclinic phases are involved, such an approach is practically impossible, and an approximated treatment has been proposed, based on the observation that in those cases there are shear strains almost linearly coupled to the transverse component of P, implying a divergence of the Curie-Weiss type in the associated compliances. Here the argument is extended to the general case of transitions whose major effect is a rotation of the polarization, and the limits of its validity are discussed. As experimental verification, the elastic response of BaTiO3 is measured and analyzed, together with those of other ferroelectric perovskites available in the literature, such as KNN. [ABSTRACT FROM AUTHOR]

We report extended X-ray absorption fine structure measurements at the Mn K absorption edge and in a wide temperature range on La0.25Ca0.75MnO3 samples with a charge ordering transition temperature, TCO of the Mn3+ and Mn4+ ions around 225 K. The mean Mn–O distances do not show major changes at the transition; however, our results show the presence of an anomalous local lattice disorder and distortion below TCO, possibly determined by the breaking of the symmetries of the high temperature state, that is the splitting of the Mn–O distances. [Copyright &y& Elsevier]

Depolarization in ferroelectric materials limits their piezoelectric applications and needs careful calibration for device constructions. With BaTiO 3 and PbSc 0.5 Ta 0.5 O 3 as prototypic ferroelectrics we demonstrate how to apply Resonant Piezoelectric Spectroscopy, RPS, to measure the direct and the converse piezoelectric effects as a function of temperature to detect depolarization via the collapse of the piezoelectric effect and the anomaly of elastic moduli. Comparison of the RPS data with in-situ d 33 measurements on a BaTiO 3 ceramic shows that the temperature evolution of the longitudinal piezoelectric coefficient d 33 can be determined with high accuracy. This makes RPS a complementary and convenient method for the investigation of polar phase transitions and the thermal evolution of the piezoelectric effect. Finally, the observation of an elastic anomaly concomitant to depolarization indicates that elastic measurements are an indirect means to measure the depolarization temperature in ferroelectrics. • RPS is a versatile and complementary technique for measuring depolarization in ferroelectrics with the ability for in-situ poling. • RPS can accurately measure the thermal evolution of the longitudinal piezoelectric coefficient d 33 , which is important for many technological applications. • Elastic measurements are an indirect means to measure the depolarization temperature in ferroelectrics. [ABSTRACT FROM AUTHOR]