Anelastic Measurements Research Articles

Phase Transition and Dynamics of Defects in the Molecular Piezoelectric TMCM-MnCl3 and the Effect of Partial Substitutions of Mn

We present dielectric and anelastic spectroscopy measurements of the molecular piezoelectric TMCM-MnCl3 and TMCM-Mn0.95M0.05Cl3 (M = Cu, Fe, Ni; TMCM = trimethylchlorometylammonium), whose powders were pressed into discs and bars and deposited as films on Si by Matrix-Assisted Pulsed Laser Evaporation (MAPLE). As in other molecular ferroelectrics, the dielectric permittivity ϵ′ drops at the structural transition temperature TC, below which the number of directions that the polar TMCM molecules visit is reduced, with the formation of ferroelectric domains. Concomitantly, the Young’s modulus E starts increasing and the elastic energy loss has a step-like increase, attributable to the motion of the domain walls. Both the dielectric and elastic anomalies indicate the improper character of the ferroelectric transition, where the ordering of the molecular orientations is not driven by the cooperative interaction of their electric dipoles. Below room temperature, at least two thermally activated relaxation processes appear both in the dielectric and anelastic spectra, whose real and imaginary parts measured at several frequencies can be fit with the Havriliak–Negami formula. The microscopic parameters so-obtained indicate that they are due to point defects, and it is argued that they are Cl vacancies and their complexes with TMCM vacancies. The considerable width of these relaxation maxima is explained by the geometry of the hexagonal perovskite structure. The partial substitution of Mn with 5% Ni has little effect on the anelastic and dielectric spectra, while Cu and, especially, Fe cause a large enhancement of the losses attributed to domain wall relaxation, with substantial contributions also above TC. The condensation of water from the humidity in the powders compacted by cold pressing was observed and discussed. The piezoelectric activity of the films was assessed by PFM.

Exploration of the best reference material on anelastic measurement by cyclic loading under high pressure

ABSTRACT Anelastic measurement by cyclic loading under high pressure has been developed by means of in situ X-ray observation at a synchrotron facility. In this method, the reference material is a key factor to precisely determine attenuation and moduli of unknown materials. We compared the performance of three types of reference materials (dense polycrystalline alumina, alumina single-crystal parallel to c-axis, and flexible graphite) under the pressure of 3 GPa and the temperature range between 1173 and 1373 K. The phase lags of strain between reference materials and samples show that the flexible graphite is less attenuated than dense polycrystalline alumina and alumina single crystal in various periods. The strain ratios show that the flexible graphite is much softer and can produce the measurable strain in the limited displacement. The flexible graphite, as reference material, is more excellent to detect the relatively lower energy dispersion of mantle minerals at high pressure.

Flexible lead-free NBT-BT/PVDF composite films by hot pressing for low-energy harvesting and storage

The idea of this work is finding the way to efficiently and safely use mechanical energy released in small quantities around us to power up small-scale electronic devices used in everyday life. To this purpose, flexible lead-free piezoelectric composite films were prepared by hot pressing. Different amounts (30, 35 and 40 vol%) of lead-free piezoelectric material bismuth sodium titanate-barium titanate were embedded in the matrix of polyvinylidene fluoride under carefully optimized conditions of temperature and pressure, obtaining flexible films with quite homogeneous distribution of piezo-active filler. ATR-FTIR analysis revealed that hot pressing the flexible films caused a transformation of electro-inactive PVDF α-phase into electro-active β and γ phases. Dielectric measurements showed an increase of the permittivity up to 80 with the active phase increasing. Anelastic measurements showed that the elastic modulus increases as well with the fraction of active ceramic phase. Lastly, obtained flexible polymer-composites demonstrated notable properties both for energy storage and energy harvesting application, showing up to 74% of energy storage efficiency and, from testing of the force impact, up to 9 V and ~ 80 μW of output voltage and power.

Cation reorientation and octahedral tilting in the metal-organic perovskites MAPI and FAPI

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 PbI6 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.

Stability of Cubic FAPbI3 from X-ray Diffraction, Anelastic, and Dielectric Measurements.

Among the hybrid metal-organic perovskites for photovoltaic applications, FAPbI3 (FAPI) has the best performance regarding efficiency and the worst regarding stability, even though the reports on its stability are highly contradictory. In particular, since at room temperature the cubic α phase, black and with high photovoltaic efficiency, is metastable against the yellow hexagonal δ phase, it is believed that α-FAPI spontaneously transforms into δ-FAPI within a relatively short time. We performed X-ray diffraction and thermogravimetric measurements on loose powder of FAPI, and present the first complete dielectric and anelastic spectra of compacted FAPI samples under various conditions. We found that α-FAPI is perfectly stable for at least 100 days, the duration of the experiments, unless extrinsic factors induce its degradation. In our tests, degradation was detected after exposure to humidity, strongly accelerated by grain boundaries and the presence of δ phase, but it was not noticeable on the loose powder kept in air under normal laboratory illumination. These findings have strong implications on the strategies for improving the stability of FAPI without diminishing its photovoltaic efficiency through modifications of its composition.

On the proposed martensitic-like structural transformation in V, Nb, and Ta

The transition metals Nb, Ta and V have been known to be cubic at all temperatures, until recently the existence of a martensitic transformation has been reported, based on anomalies in the thermal expansion at low temperatures. Such a structural transformation would have passed unnoticed, because it would be hindered by small amounts of impurities. This finding is discussed in the light of anelastic measurements on Nb samples whose purities are comparable to those presenting the dilatometric anomalies. It results that the effects of the alleged transformation on the anelastic spectra would be at least three orders of magnitude smaller than in typical mar- tensitic transformations. A possible alternative explanation for the observed anomalies is proposed in terms of precipitation of unnoticed residual H.

Multiferroic (Nd,Fe)-doped PbTiO3 ceramics with coexistent ferroelectricity and magnetism at room temperature

We report the structural, dielectric, elastic, ferroelectric and ferromagnetic properties of multiferroic (Nd, Fe)-doped PbTiO3 perovskite ceramics with composition (Pb0.88Nd0.08)(Ti0.94Fe0.04Mn0.02)O3, prepared by different solid state reaction methods: the first one based on a single-stage calcination (Method I) and the second based on a double-stage calcination (Method II). Structural, dielectric and anelastic measurements evidenced a double phase transition for samples prepared by Method I, which has been attributed to phase separation. This phase separation has been confirmed also by TEM and HRTEM investigations. Samples prepared by Method II showed a single phase transition from paraelectric to ferroelectric phase. We found coexistent ferroelectric and ferromagnetic properties, also at room-temperature, but only for ceramics prepared by Method II. The crucial role of calcination process for avoiding phase separation and obtaining homogeneous structures with ferroelectric and ferromagnetic order is underlined.

Competition between Polar and Antiferrodistortive Modes and Correlated Dynamics of the Methylammonium Molecules in MAPbI3 from Anelastic and Dielectric Measurements.

The mechanisms behind the exceptional photovoltaic properties of the metallorganic perovskites are still debated and include a ferroelectric (FE) state from the ordering of the electric dipoles of the organic molecules. We present the first anelastic (complex Young's modulus) and new dielectric measurements on CH3NH3PbI3, which provide new insight into the reorientation dynamics of the organic molecules and the reason why they do not form a FE state. The permittivity is fitted within the tetragonal phase with an expression that includes the coupling between FE and octahedral tilt modes, indicating that the coupling is competitive and prevents FE ordering. The onset of the orthorhombic phase is accompanied by sharp stiffening, analogous to the drop of permittivity, due to the hindered molecular dynamics. On further cooling, an intense anelastic relaxation process without a dielectric counterpart suggests the reorientation of clusters of molecules with strong antiferroelectric correlations.

On the underlying micromechanisms in time-dependent anelasticity in Al-(1 wt%)Cu thin films

This paper reveals potential micro mechanisms underlying time-dependent anelasticity observed in Al-(1 wt%)Cu thin films. The analyzed deformation mechanisms involve dislocation motion and interaction with solute diffusion, grain boundaries and precipitates. In order to investigate the role of these mechanisms, Al-(1 wt%)Cu alloy thin films are heat treated to systematically change the precipitation state, while characterizing the grain boundary distribution with electron backscatter diffraction. Micromechanical characterization is performed by microbeam bending, nano-tensile creep testing and nano-indentation. Results in microbeam bending reveal, for all precipitate and grain boundary states considered, a similar time-dependent evolution of the anelastic strain after load release. The magnitude of the recovered strain is also observed to be independent of the precipitate or grain boundary configuration. The nano-tensile creep test also indicates the same time-dependent anelastic evolution, indicating that the loading state does not affect the underlying mechanisms. Analysis of strain bursts in nano-indentation shows that pinning of dislocations by Cu solutes is unaffected by the precipitation state. Based on uniaxial creep and time-dependent anelasticity measurements in pure Al specimens, it is made plausible that the time-dependent anelasticity originates from diffusion-limited glide or climb of dislocation segments that are pinned at Cu solutes or in dislocation structures, which provide an internal driving force.

Elastic aging from coexistence and transformations of ferroelectric and antiferroelectric states in PZT

Materials undergoing antiferroelectric/ferroelectric (AFE/FE) transitions are studied for possible applications that exploit the large volume, charge, and entropy differences between the two states, such as electrocaloric cooling, energy storage, and electromechanical actuators. Though certain compositions of PbZr1−xTixO3 codoped with La and Sn may withstand millions of electrically induced AFE/FE cycles, in other cases few thermally induced cycles and room temperature aging may cause noticeable changes in the material properties. This is particularly evident in the elastic moduli, which at room temperature can become as much as four times softer. In order to get more insight into the mechanisms involved in such elastic aging and full recovering with mild annealing at 600–800 K, the effect of La doping on PbZr0.954Ti0.046O3 is studied with anelastic measurements. Complete suppression of the time dependent phenomena is found after the transformation of the intermediate FE phase into incommensurate AFE by 2% La doping. This is discussed in terms of disappearance of the stress and electric fields at the FE/AFE interfaces, in the light of the thermally activated anelastic relaxation processes that are observed at high temperature and are due to mobile defects, presumably O vacancies.

Influence of diffuse phase transition on the anelastic behavior of Nb-doped Pb(Zr0.53Ti0.47)O3 ceramics

In this study, we investigated the possible physical mechanisms giving rising to thermally activated anelastic relaxations in Nb-doped Pb(Zr0.53Ti0.47)O3 ceramics, at temperatures below the ferro-paraelectric phase transition. The dielectric analysis showed a ferro-paraelectric diffuse phase transition, extended over a wide temperature range, but without relaxor behavior. From the anelastic measurements, three regions with anomalies were identified. The mechanisms involved with anomalies between 300–570 K had been previously investigated for Pb(ZrxTi1−x)O3-based materials. However, the responsible mechanisms by the other anelastic relaxation peak, at 596 K, are controversial. The results and analysis described here show that this peak can be related to the freezing of the polar regions or to the strong pinning of ferroelectric clusters and domains, which are responsible for the observed diffuse phase transition in this ferroelectric material.

Refining the phase diagram of Pb1−xLax(Zr0.9Ti0.1)1−x/4O3 ceramics by structural, dielectric, and anelastic spectroscopy investigations

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 (0 < x < 0.04). From structural analysis and polarization-electric field measurements, we have found that the ground state of PLZT samples with x < 0.025 is rhombohedral R3c, while samples with x > 0.032 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.

Phase Transitions Of The Ferroelectric Na0.5Bi0.5TiO3 By Dielectric And Internal Friction Measurements

This work focuses on the high temperature dielectric and mechanical spectroscopic properties of lead free relaxor Sodium Bismuth Titanate (NBT) ceramics, fabricated by conventional ceramic double sintering method. Systematic measurements of dielectric and mechanical properties have been performed as a function of temperature. A sequence of phase transitions has been studied by both dielectric and anelastic measurements. Three internal friction peaks were observed near 350, 200 and 120 °C. The 350 °C-peak corresponds to a transition associated with the tetragonal (P4bm) to rhombohedral (R3c) phase, and the 200 °C-peak is related to the ferroelectric to antiferroelectric phase transition. The 120 °C-peak could be ascribed to the interaction between the domain walls and the diffusion of oxygen vacancies in the domains. Copyright © 2015 VBRI Press.

Diffusion of Oxygen in Ti-15Mo-xZr Alloys Studied by Anelastic Spectroscopy

Because of their low elasticity modulus, titanium alloys have excellent biocompatibility, and are largely used in orthopedic prostheses. Among the properties that are beneficial for use in orthopedic implants is the elasticity modulus, which is closely connected to the crystal structure of the material. Interstitial elements, such as oxygen, change the mechanical properties of the material. Anelastic spectroscopy measurements are a powerful tool for the study of the interaction of these elements with the metallic matrix and substitutional solutes, providing information on the diffusion and concentration of interstitial elements. In this study, the effect of oxygen on the anelastic properties of alloys in the Ti-15Mo-Zr system was analyzed using anelastic spectroscopy measurements. The diffusion coefficients, pre-exponential factors, and activation energies of these alloys were calculated for oxygen.

Nitrogen Diffusion in Niobium under Low Pressure

The interaction among heavy interstitial atoms present in metals with bcc structure is studied using anelastic spectroscopy. This technique makes it possible to obtain information on interstitial concentration, precipitation, solubility limit, and diffusion. The diffusion coefficients of nitrogen in niobium were obtained using the relaxation parameters obtained from anelastic spectroscopy measurements for different oscillation frequencies of the system. The results showed the interstitial diffusion of nitrogen present in solid solution in niobium when submitted to different charges of nitrogen at a temperature of 1373 K and a partial pressure in the order of 10-4Torr. The exponential variation of the pressure experimentally in function of the time was thus obtained.

Effects of coupling between octahedral tilting and polar modes on the phase diagram of the ferroelectric perovskites PbZr1−xTixO3 and (Na1/2Bi1/2)1−xBaxTiO3

Recent anelastic and dielectric spectroscopy measurements revealed new features of the phase diagram of PbZrTiO regarding the manner in which various ferroelectric and octahedral tilt instability lines approach each other. Rather than crossing, they tend to merge, also after considerable bending, and give rise to combined polar/tilt transitions over extended concentration ranges. The same effect is also found in (NaBi)BaTiO. It is proposed that such a behaviour results from cooperative coupling between the polar and tilt modes, and could be explained by a mechanism similar to that proposed by Holakowski in 1973, where coupling of two-order parameters with different symmetries produces a transformation of mixed character. The possible reasons are also discussed why disordered tilting, proposed to occur in correspondence with an elastic stiffening near the antiferroelectric/ferroelectric border in PZT, would be particularly difficult to reveal by diffraction.

Normal mode splitting function measurements of anelasticity and attenuation in the Earth’s inner core

We have used the iterative spectral fitting method to measure both the elastic and anelastic splitting functions of 20 inner core sensitive normal modes. These modes show significant improvement in spectral fit when anelastic splitting function coefficients dst are introduced in addition to the elastic splitting function coefficients cst. We employ two separate anelastic treatments: (i) fully anelastic measurement, in which a complete set of anelastic splitting function coefficients is measured in addition to the elastic coefficients, and (ii) zonal anelastic measurement, in which anelasticity is only allowed in zonal splitting function coefficients. Together, these two approaches confirm that normal modes sensitive to the Earth’s inner core resolve zonally dominant elastic and anelastic structures. The zonal dominance of anelasticity suggests that the inner core exhibit cylindrical attenuation anisotropy in addition to cylindrical velocity anisotropy. In particular, the zonally dominant anelasticity correlates with zonal elastic structure, that is, directions of higher velocity in the inner core also appear more attenuating.

Rotational dynamics in ammonia borane: Evidence of strong isotope effects

Abstract This work reports anelastic spectroscopy measurements on the partially deuterated (ND3BH3 and NH3BD3) and perdeuterated (ND3BD3) ammonia borane (NH3BH3) compounds. The relaxations previously reported in NH3BH3 are observed in all the samples, and are ascribed to the rotational and torsional dynamics of NH(D)3BH(D)3 complexes. A new thermally activated peak appears at 70 K (for a vibration frequency of ∼1 kHz) in the spectrum of NH3BD3 and ND3BD3. The peak is practically a single-time Debye process, indicating absence of interaction between the relaxing units, and has a strikingly high intensity. A secondary relaxation process is also detected around 55 K. The anelastic spectrum of the ND3BH3 only displays this less intense process at 55 K. The analysis of the peaks supplies information about the dynamics of the relaxing species, and the obtained results provide indications on the effect of partial and selective deuteration on the hydrogen (deuterium) dynamics.

Merging of the polar and tilt instability lines near the respective morphotropic phase boundaries of PbZr1−xTixO3

The results are presented of anelastic and dielectric spectroscopy measurements on large grain ceramic PZT with compositions near the two morphotropic phase boundaries (MPBs) that the ferroelectric (FE) rhombohedral phase has with the Zr-rich antiferroelectric and Ti-rich FE tetragonal phases. These results are discussed together with similar data from previous series of samples, and reveal new features of the phase diagram of PZT, mainly connected with octahedral tilting and its coupling with the polar modes. Additional evidence is provided of what we interpret as the onset of the tilt instability, when is initially frustrated by lattice disorder, and the long range order is achieved at lower temperature. Its temperature T_IT(x) prosecutes the long range tilt instability line T_T(x) up to T_C, when T_T. It is proposed that the difficulty of seeing the expected 1/2<111> modulations in diffraction experiments is due to the large correlation volume associated with that type of tilt fluctuations combined with strong lattice disorder. It is shown that the lines of the tilt instabilities tend to be attracted and merge with those of polar instabilities. Not only T_IT bends toward T_C and then merges with it, but in our series of samples the temperature T_MPB of the dielectric and anelastic maxima at the rhombohedral/tetragonal MPB does not cross T_T, but deviates remaining parallel or possibly merging with T_T. These features, together with a similar one in NBT-BT, are discussed in terms of cooperative coupling between tilt and FE instabilities, which may trigger a common phase transition. An analogy is found with recent simulations of the tilt and FE transitions in multiferroic BiFeO3. An abrupt change is found in the shape of the anelastic anomaly at T_T when x passes from 0.465 to 0.48, possibly indicative of a rhombohedral/monoclinic boundary.

Antiferromagnetic and Ferroelectric Phase Transitions and Instabilities in PFW-PT Multiferroic Solid Solution Characterized by Anelastic Measurement

Magnetic, electric and mechanical behaviors are strongly coupled, but only a few models are able to describe electro-magneto-mechanical coupling effects. In this work, multiferroic solid solutions between Pb(Fe2/3W1/3)O3 (PFW) and PbTiO3 (PT) [PFW-PT] have been characterized by anelastic measurements. Anomalies in the temperature dependence of the elastic constants have been observed at TN and TC for all samples, indicating that the magnetoelectric coupling (ME) between the ferroelectric and antiferromagnetic orders occurs “via strain.” A phase diagram was established, comparing magnetic and dielectric measurements.