Elastic Anomalies Research Articles

A new order parameter model for the improper ferroelastic phase transitions in KMnF3 single crystal.

This paper proposes a new order parameter model which satisfactorily explains complicated symmetry changes, the temperature-pressure (T-P) phase diagram and elastic anomalies observed experimentally with the improper ferroelastic phase transitions in multiferroic KMnF3 single crystal. First, it is shown that the order parameter model is transformed according to the four-dimensional reducible representation of the wavevector star channel group. Second, based on the order parameter model and the singularity theory, the sixth-order structurally stable Landau potential model is constructed. Finally, the theoretical T-P phase diagram is plotted and the elastic anomalies possible for each of the phase transitions are discussed.

Elastic properties and microstructure evolution of Zn2SnO4-spinel-containing composite ceramics based on tin oxide and zinc oxide

Ceramics based on tin oxide (SnO2) and zinc oxide (ZnO) were sintered at temperatures up to 1400 °C. Except for the end members, all these ceramics are two- or three-phase composites containing spinel phase (Zn2SnO4). Similar to pure SnO2 ceramics, also the spinel-rich composite (50:50 mixture) does not exhibit densification after sintering at 1400 °C. Spinel Zn2SnO4 is formed in all composites, with a major increase of spinel content at around 1000 °C. Young’s modulus values, determined via impulse excitation, are between the exponential relation for convex pores and a benchmark relation for concave pores (or a percolation relation). The evolution of Young’s modulus during sintering reveals significant differences between SnO2 (weak increase above 1000 °C), ZnO (significant increase above 800 °C) and the composites (intermediate). Spinel formation is revealed during heating by a distinct peak (elastic anomaly) at around 1000 °C.

Elastic anomalies across the P21mn→Pnnm structural phase transition in δ-(Al,Fe)OOH

Abstract Hydrogen may be recycled into the Earth's lower mantle by subduction and stabilized in solid solutions between phase H (MgSiO4H2), δ-AlOOH, ε-FeOOH, and SiO2 post-stishovite. In high-pressure oxyhydroxide phases, hydrogen is incorporated following the typical (OHO) sequence, adopting the asymmetric configuration O-H···O that evolves into a symmetric disordered state upon compression. Moreover these iron-/aluminum-bearing oxyhydroxides [δ-(Al,Fe)OOH] present a structural phase transition from P21nm to Pnnm as pressure increases. Here, the single-crystal elasticity of the P21nm phase of δ-(Al0.97,Fe0.03)OOH has been experimentally measured across the P21nm→Pnnm transition up to 7.94(2) GPa by simultaneous single-crystal X-ray diffraction (XRD) and Brillouin spectroscopy at high pressures. The transition appears to be continuous, and it can be described with a second, fourth and six order terms Landau potential. Our results reveal an enhanced unit-cell volume compressibility, which is linked to an increase of the b- and a-axes linear compressibility in the P21nm phase of δ-(Al0.97,Fe0.03)OOH prior to the transition. In addition, we observed the presence of elastic softening in the P21nm phase that mostly impacts the elastic stiffness coefficients c12, c22 and c23. The observed elastic anomalies cause a significant change in the pressure dependence of the adiabatic bulk modulus (KS). These results provide a better understanding of the relation between elasticity, P21mn→Pnnm structural phase transition and hydrogen dynamics in δ-(Al0.97,Fe0.03)OOH, which may be applied to other O-H···O-bearing materials.

Theoretical study of structural phase transition and soft mode behavior in moganite

Changes in the structure and lattice dynamics of the moganite during crystal expansion were studiedusing ab initio calculations within the framework of density functional theory. The results obtained shed light onmany anomalies in the temperature behavior of this crystal, such as the presence of a phase transition, soft modecondensation, elastic anomalies and negative thermal expansion. Comparison of the structural and dynamicproperties of moganite and quartz opens up new possibilities for their identification in natural samples of mixedcomposition.

Temperature dependence of Young’s modulus and the occurrence of an elastic anomaly in porous alumina-mullite composites prepared by starch consolidation casting

The temperature dependence of Young’s modulus has been measured by impulse excitation up to 1400 °C (heating and cooling) for alumina-mullite composites with 40–60 wt% alumina prepared by starch consolidation casting, after firing at 1570 °C, resulting in materials with high porosities (43–57 %). Using previously determined temperature master curves, both analytical predictions and numerical computations on computer-generated microstructures are compared with experimental data, resulting in excellent agreement for the alumina-mullite composites. Apart from the overall decrease of Young’s modulus during heating, an elastic anomaly starting at around 950 °C and cumulating at around 1050 °C is observed in all cases during heating (but not during cooling), and is shown to be stronger with increasing alumina content and porosity. The results are discussed in terms of a “glass phase hypothesis” and a “phase transition hypothesis”, although neither of them provides a satisfactory explanation of the observed phenomenon.

Ultrasonic investigation of the elastic properties of the approximant GdCd6

We have investigated complementarily the magneto-elastic coupling in the approximant GdCd6 by measuring the temperature and magnetic field dependence of the longitudinal elastic constant C11. A pronounced elastic softening toward the phase transition temperature Ts= 156 K was observed in the temperature dependence of the C11, suggesting the presence of a structural phase transition. Furthermore, anomalous elastic behavior was observed in the temperature dependence of the C11 below 20 K, closely related to the already known consecutive magnetic phase transitions. The H–T magnetic phase diagram deduced from elastic anomalies appearing at the different phase transitions are consistent with our previous data of the other independent elastic constants CE= (C11−C12)/2 and C44 for a cubic crystal. We argue the origin of the structural phase transition and low temperature elastic property including a possible origin of such a rich variety of magnetic phases.

Monitoring the ferroelectric phase transition of barium titanate ceramics via impulse excitation

Impulse excitation is a suitable tool to determine the temperature dependence of Young’s modulus and to monitor the ferroelectric phase transition of unpoled barium titanate ceramics (tetragonal-to-cubic and vice versa). By measurement from room temperature to 200–300 °C and back, it is found that there is an elastic anomaly with a sharp minimum (at 120 °C during heating and 110 °C during cooling, with a completely reproducible hysteresis), below and above which Young’s modulus exhibits values of 40–50 GPa and up to 90 GPa, respectively, and damping changes abruptly from values of order 0.01 to less than 0.001.

Two novel homozygous variants of ATP6V0A2 and ALDH18A1 lead to autosomal recessive cutis laxa type 2 and 3 in two Pakistani families.

Autosomal recessive cutis laxa type 2A (ARCL2A; OMIM: 219200) is characterized by neurovegetative, developmental and progeroid elastic skin anomalies. It is caused by biallelic variation in ATPase, H+ transporting V0 subunit A2 (ATP6V0A2; OMIM: 611716) located on chromosome 12q24.31. Autosomal recessive cutis laxa type 3A (ARCL3A; OMIM: 219150) is another subclinical type characterized by short stature, ophthalmological abnormalities and a progeria-like appearance. The ARCL3A is caused by loss of function alterations in the aldehyde dehydrogenase 18 family member A1 (ALDH18A1; OMIM: 138250) gene located at chromosome 10q24.1. Whole-exome sequencing (WES), and Sanger sequencing were performed for molecular diagnosis. 3D protein modeling was performed to investigate the deleterious effect of the variant on protein structure. In this study, clinical and molecular diagnosis were performed for two families, ED-01 and DWF-41, which displayed hallmark features of ARCL2A and ARCL3A, respectively. Three affected individuals in the ED-01 family (IV-4, IV-5 and V-3) displayed sagging loose skin, down-slanting palpebral fissures, excessive wrinkles on the abdomen, hands and feet, and prominent veins on the trunk. Meanwhile the affected individuals in the DWF-41 family (V-2 and V-3) had progeroid skin, short stature, dysmorphology, low muscle tone, epilepsy, lordosis, scoliosis, delayed puberty and internal genitalia. WES in the index patient (ED-01: IV-4) identified a novel homozygous deletion (NM_012463.3: c.1977_1980del; p.[Val660LeufsTer23]) in exon 16 of the ATP6V0A2 while in DWF-41 a novel homozygous missense variant (NM_001323413.1:c.1867G>A; p.[Asp623Asn]) in exon 15 of the ALDH18A1 was identified. Sanger validation in all available family members confirmed the autosomal recessive modes of inheritances in each family. Three dimensional in-silico protein modeling suggested deleterious impact of the identified variants. Furthermore, these variants were assigned class 1 or "pathogenic" as per guidelines of American College of Medical Genetics 2015. Screening of ethnically matched healthy controls (n= 200 chromosomes), excluded the presence of these variations in general population. To the best of our knowledge, this is the first report of ATP6V0A2 and ALDH18A1 variations in the Pakhtun ethnicity of Pakistani population. The study confirms that WES can be used as a first-line diagnostic test in patients with cutis laxa, and provides basis for population screening and premarital testing to reduce the diseases burden in future generations.

Low-temperature and elastic properties of the 1/1 Tsai-type quasicrystal approximant GdCd6 investigated by ultrasonic measurements

Low-temperature and elastic properties of the quasicrystal approximant GdCd6 have been investigated by means of an ultrasonic measurement. Salient elastic anomalies were observed in the temperature and magnetic field dependence of the principal elastic constants, most probably being associated with the successive multiple magnetic phase transitions showing up at low temperatures. Based on the experimental data, a magnetic field vs temperature phase diagram was constructed. In a zero magnetic field, at least four phases appear to exist. However, the phase diagram both for the magnetic field applied for H// and H// is richer, and interestingly some phase boundaries correspond to the development of field-induced phases, leading to the intricate magnetic phase diagram possibly with multiple ordered phases. We discuss the elastic and electronic properties at low temperatures, and also the nature of the multiple magnetic phase transitions of GdCd6.

Brillouin Scattering Study of Ferroelectric Instability of Calcium–Strontium–Barium Niobate Single Crystals

Uniaxial ferroelectrics with tetragonal tungsten bronze structure are important functional materials with photorefractive, electrooptic, piezoelectric, and pyroelectric properties. SrxBa1-xNb2O6 (SBN100x) with x > 50 is known as a typical uniaxial relaxor ferroelectric, while CaxBa1-xNb2O6 (CBN100x) undergoes nearly normal ferroelectric phase transitions. Single crystals of CSBN100x = [x(CBN28) + (1 - x) (SBN61)] = xCa0.28Ba0.72Nb2O6 + (1 - x) Sr0.61Ba0.39Nb2O6 with nominal x = 0.00, 0.25, 0.50, 0.75, and 1.00 were studied to clarify the dynamical properties at the crossover from relaxor (x = 0) to normal (x = 1) ferroelectric behavior. The longitudinal acoustic (LA) and transverse acoustic (TA) modes and a central peak (CP) related to the relaxation process of polarization fluctuations along the polar c-axis were studied in uniaxial ferroelectric CSBN single crystals as a function of temperature via Brillouin scattering spectroscopy. A CBN28 (x = 1.00) crystal shows the sharp elastic anomaly of the LA mode in the gigahertz range toward Curie temperature, Tc. However, those of CSBN25 (x = 0.25) and SBN61 (x = 0.00) crystals show diffusive anomalies due to stronger random fields. The relaxation time determined from the width of a CP shows a critical slowing down in the vicinity of Tc. The elastic anomaly and slowing down of relaxation time of CSBN100x crystals become diffusive in the vicinity of Tc as the CBN28 content decreases. The origin of the crossover from relaxor to normal ferroelectric phase transitions is discussed in terms of the difference in the A1 and A2 sites' occupancies.

Phase diagram and thermoelastic property of iron oxyhydroxide across the spin crossover under extreme conditions

Spin transition and its effect on the physical properties of iron-bearing minerals at high pressure-temperature $(P\text{\ensuremath{-}}T)$ are of great importance for understanding the structural heterogeneity of Earth's mantle. Here, we investigate the phase diagram and thermoelastic properties of iron oxyhydroxide (FeOOH) across the spin crossover using dynamic high $P\text{\ensuremath{-}}T$ experiments and theoretical simulations. The Hugoniot equation of state in FeOOH has been measured up to $\ensuremath{\sim}90$ GPa and $\ensuremath{\sim}2100$ K in a two-stage light-gas gun and exhibits a density discontinuity between 47 GPa (\ensuremath{\sim}950 K) and 61 GPa (\ensuremath{\sim}1150 K) due to the high-low spin transition of ${\mathrm{Fe}}^{3+}$, which is consistent with our first-principles calculations. The $P\text{\ensuremath{-}}T$ phase diagram indicates that the shock-elevated temperature shifts the spin transition to a higher pressure and broadens the pressure range of mixed spins. The large volume collapse of FeOOH during its spin crossover leads to remarkable elastic anomalies, with \ensuremath{\sim}60% softening of adiabatic bulk modulus and a negative Poisson's ratio (\ensuremath{-}0.1) of abnormal auxeticity in the mixed-spin phase. Our results suggest that FeOOH undergoes an unselective spin transition of ferric iron at the corresponding $P\text{\ensuremath{-}}T$ conditions of the Earth's 1400--1800 km depth and exhibits drastic softening in sound velocities and elastic modulus which may be detected as seismic heterogeneities in subducting slabs of the lower mantle.

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.

Strange Elastic Anomalies With Ultraslow Dynamics Around Magnetic Critical Endpoint

Near the magnetic critical endpoint of UCoAl, peculiar elastic anomalies exhibiting exotic ultraslow dynamics arising from electric quadrupoles are indicated. Combining this with diverse fluctuations, intriguing phenomena and exotic ground states are expected

Recent Progress in Phase Stability and Elastic Anomalies of Group VB Transition Metals

Recently discovered phase transition and elastic anomaly of compression-induced softening and heating-induced hardening (CISHIH) in group VB transition metals at high-pressure and high-temperature (HPHT) conditions are unique and interesting among typical metals. This article reviews recent progress in the understanding of the structural and elastic properties of these important metals under HPHT conditions. Previous investigations unveiled the close connection of the remarkable structural stability and elastic anomalies to the Fermi surface nesting (FSN), Jahn–Teller effect, and electronic topological transition (ETT) in vanadium, niobium, and tantalum. We elaborate that two competing scenarios are emerging from these advancements. The first one focuses on phase transition and phase diagram, in which a soft-mode driven structural transformation of BCC→RH1→RH2→BCC under compression and an RH→BCC reverse transition under heating in vanadium were established by experiments and theories. Similar phase transitions in niobium and tantalum were also proposed. The concomitant elastic anomalies were considered to be due to the phase transition. However, we also showed that there exist some experimental and theoretical facts that are incompatible with this scenario. A second scenario is required to accomplish a physically consistent interpretation. In this alternative scenario, the electronic structure and associated elastic anomaly are fundamental, whereas phase transition is just an outcome of the mechanical instability. We note that this second scenario is promising to reconcile all known discrepancies but caution that the phase transition in group VB metals is elusive and is still an open question. A general consensus on the relationship between the possible phase transitions and the mechanical elasticity (especially the resultant CISHIH dual anomaly, which has a much wider impact), is still unreached.

Magnetoelastic coupling behaviour of nanocrystalline ε-Fe2O3

Preparation of a ceramic sample which preserved the nanoscale grain sizes of ∼10–30 nm has allowed elastic and anelastic properties of ε-Fe2O3 to be investigated as functions of temperature and magnetic field strength by Resonant Ultrasound Spectroscopy in the frequency range ∼0.1–1 MHz. Formal analysis of spontaneous strains, e, from previously obtained high resolution lattice parameter data confirmed that magnetic ordering below ∼500 K is accompanied by strains of up to ∼±0.002 due to coupling with the order parameter, m, according to λem2. However, this coupling does not result in elastic softening that would be expected if the order parameter relaxed in response to an induced strain on the timescale of the acoustic resonances. Stiffening or softening during heating through ∼450–480 K of the initial as prepared material, which acquired a distinct magnetisation parallel to the stress applied during Spark Plasma Sintering, is attributed to changes in magnetic domain configurations involving preferred local alignments of individual moments of monodomain crystals. The crystallographic space group, Pna21, and magnetic space group at room temperature, Pna'21', allow ε-Fe2O3 to be both piezoelectric and piezomagnetic. It is postulated that changes in the effective coefficients of these properties for bulk samples are responsible for the observed variations in acoustic resonance frequencies according to the magnetic domain structure present. No elastic or anelastic anomalies were observed at the commensurate-incommensurate transition near 110 K. Instead, acoustic resonance frequencies changed in response to an applied magnetic field, consistent with viscous motion of magnetic domain walls and the effect of poling on piezo coefficients. Ceramic samples of ε-Fe2O3 could have potentially functional piezoelectric and/or piezomagnetic properties that are tunable by choice of magnetic and thermal history.

Symmetry-resolved elastic anomalies in spin-crossover cobaltite LaCoO3

Ultrasound velocity measurements of the pseudo-cubic spin-crossover cobaltite LaCoO$_3$ and the lightly Ni-substituted La(Co$_{0.99}$Ni$_{0.01}$)O$_3$ reveal two types of symmetry-resolved elastic anomaly in the insulating paramagnetic state that are commonly observed in these compounds. The temperature dependence of the bulk modulus exhibits Curie-type softening upon cooling below 300 K down to $\sim$70 K, indicating the presence of isostructural lattice instability arising from orbital fluctuations. The temperature dependence of the tetragonal and trigonal shear moduli exhibits unusual hardening upon cooling below 300 K, indicating the occurrence of elasticity crossover arising from the spin crossover. The present study also reveals that the isostructural lattice instability in LaCoO$_3$ is sensitively suppressed with the Ni substitution, indicating the suppression of orbital fluctuations with the light Ni substitution. This Ni substitution effect in LaCoO$_3$ can be explained on the basis that the isostructural lattice instability arises from the coupling of the lattice to the Co spin state fluctuating between the high-spin state and intermediate-spin state.

Resonant ultrasound spectroscopy for characterization of lattice instability of shape memory alloys

Shape memory alloys (SMAs) are materials able to undergo reversible displacive transitions between different crystal lattices. This ability is reflected by the elastic constants of the individual phases, as certain combinations of these constants exhibit anomalous softening when the crystal approaches the transformation temperature or when the lattice is destabilized by the presence of mobile interfaces. The lecture will summarize the advantages of using resonant ultrasound spectroscopy (RUS), and in particular its contact-less laser-based modification, for detecting and evaluating these elastic anomalies. Three recently studied cases will be discussed: i) single crystals of ferromagnetic shape memory alloys in which the instability-induced softening couples with magnetoelasticity; ii) fine regular laminates in tetragonal martensitic lattices in which the soft combinations of the elastic constants have to be calculated from the effective elastic response of the microstructure; iii) modulated crystals with highly mobile interfaces that act as strongly-nonlinear mechanical oscillators and where the properties of the interfaces can be achieved by analyzing the non-linearity.

Visualization of the disordered structure of Fe-Ni Invar alloys by reverse monte carlo calculations

Reverse Monte Carlo (RMC) calculation was performed to visualize the atomic arrangement in a disordered Fe55Ni45 alloy, which is classified as an intermediate structure between the non-crystalline glass and crystalline structures. The optimized structure of the ferromagnetic phase at low pressures revealed that Fe and Ni atoms were displaced from a perfect fcc lattice to elongate the nearest neighboring Fe-Fe atomic pairs, therefore, Fe-Fe atomic pairs have longer bond length than Fe-Ni and Ni-Ni atomic pairs. Because the elongation becomes negligible during the pressure-induced destabilization of the ferromagnetic state, the elongation of Fe-Fe pairs is the atomic scale origin of the volume expansion due to a large magnetovolume effect. Compared with the atomic arrangement in the Fe65Ni35 Invar alloy, a relationship between Fe-Fe atomic pairs, the Invar effect and elastic anomalies in the compression curve is elucidated.

Theoretical Investigation of Magneto-Electro-Elastic Piezoelectric Phononic Crystal

We design a magneto-electro-elastic piezoelectric phononic crystal (MPPC) using a one-dimensional piezoelectric superlattice (with a 3m point group) and split-ring resonators. The effect of the split-ring resonators is to enhance the piezoelectric effect of the piezoelectric superlattices. This effect will create elastic anomalies and generate the phononic band gaps. These are first proposed theoretically. We calculate the transmission function of the MPPC through Transfer Matrix Method of the phononic crystal. By using the transmission function, we theoretically study the propagation properties of the acoustic waves in the MPPC. The mechanism for multifield coupling is analyzed. A type of phononic band gap is created, called the multifield coupling phononic band gap. We analyze the possibility of crystals as left-handed metamaterials. We also discuss some potential applications.

Normal to abnormal behavior of PbSiO3 glass: A vibrational spectroscopy investigation under high-pressure

High pressure may pave the way towards atypical phenomena and properties in glass science. Through compression, vitreous silica presents a well-established elastic anomaly (EA) and the scarcely investigated elastic modulus anomaly (EMA). In this paper, we present a study of the EMA for the densified lead metasilicate (PbSiO3) glass, despite its low silica content and lack of the classical EA. PbSiO3 glass was densified in diamond anvil cell and Belt press apparatus and analyzed by Brillouin spectroscopy and, when applicable, spectroscopic ellipsometry. The elastic modulus anomaly is characterized by a decrease in the longitudinal sound velocity of the densified glass compared to the uncompressed glass and attributed to the low glass ability to undergo significant densification. Densification pathways in PbSiO3 glass are discussed in light of in-situ Brillouin and Raman probes.