Structural Phase Transition Temperature Research Articles

Dielectric, pyroelectric and ferroelectric properties of lead-doped Sn2P2S6 crystals

ABSTRACTThe dielectric, pyroelectric and ferroelectric properties of (PbySn1−y)2P2S6 (y = 0.1, 0.2 and 0.3) single crystals were analysed in the vicinity of phase transition. The measurements were done covering a wide range of frequency (20 Hz to 1 MHz) and temperature (30350 K) range. Structural phase transition temperature decreases with increased lead concentration and evokes the broadening of the dielectric anomaly. The features of this phase transition are discussed and related to stereoactivity of Sn2+ ions and fluctuations of the concentration of Pb2+ ions. Pyroelectric measurements were performed from 190 K to 325 K during the heating cycle. These investigations showed that an increase of lead concentration does not affect the maximum value of pyroelectric coefficient, and the maximum values of pyroelectric coefficients γmax which (in the vicinity of the phase transition temperature) are nearly equal to 250 nC cm−2 K−1 for all the compositions. The temperature evolution of polarization hysteresis loops proved crystals being ferroelectrics.

Displacive structural phase transitions and the magnetic ground state of quadruple perovskite YMn7O12

We present an experimental study of the structural and magnetic phase transitions of the quadruple perovskite ${\mathrm{YMn}}_{7}{\mathrm{O}}_{12}$. On cooling below 640 K a displacive structural phase transition occurs, lowering the crystal symmetry from cubic $(Im\overline{3})$ to monoclinic $(I2/m)$, driven by long range B site ${\mathrm{Mn}}^{3+}$ orbital order. A second, unconventional structural phase transition takes place on further cooling below 200 K, which is characterized by static atomic displacements $(P{2}_{1}/n)$ as well as a dipolar-glass-like state of yttrium. This low temperature structural transition is driven by the underbonding of yttrium, which is present due to the rigid framework of octahedra tilts unique to the quadruple perovskites that primarily accommodates A site manganese ions. A ground state ferrimagnetic structure was also determined, similar to that found in other $R{\mathrm{Mn}}_{7}{\mathrm{O}}_{12}$ compounds that do not present a low temperature structural phase transition.

Study of structure and dielectric response of the ferroelectric composites (1 − x)NaNO2 + (x)KNO2 at x = 0.05, 0.1 and 0.2

The study of crystal structure temperature evolution of the ferroelectric composites (1 − х)NaNO2 + (x)KNO2 at х = 5, 10 и 20 vol. % has been performed by neutron diffraction. The temperature dependencies of the ferroelectric order parameter η(т) for sodium nitrite have been determined in the composites and pure NaNO2. They coincide on heating and cooling and do not depend on KNO2 concentration. The increasing of KNO2 structural phase transition temperature (∼10–15 K) has been revealed in the composites in comparison with pure KNO2.

Effect of oxygen content on structural, magnetic and magnetocaloric properties of (La0.7Pr0.3)0.8Sr0.2Mn0.9Co0.1O3±δ

Abstract The present study reports the effect of oxygen content on the structural, magnetic and magnetocaloric properties in the (La0.7Pr0.3)0.8Sr0.2Mn0.9Co0.1O3±δ (δ = +0.02, +0.01, −0.03) in the temperature range of 5–723 К. It has been found that the temperatures of structural phase transitions vary significantly depending on the oxygen index value, δ. In oxygen-deficient samples (δ = −0.03), two structural phase transitions are observed: O′ → O and O → R (O′ – Orbitally ordered orthorhombic phase, O – Orbitally disordered orthorhombic phase, R – Rhombohedral phase). In excess oxygen samples (δ = +0.02, +0.01), the O′-phase is not formed. The O → R transition temperature increases with decreasing δ from TO→R = 353 K (δ = +0.02) to TO→R = 623 K (δ = −0.03). Magnetic measurements show that all our compounds exhibit a paramagnetic-ferromagnetic transition at TC ∼ 205 K. The Arrott plots reveal the occurrence of a second order phase transition. It was found that the transition temperature TC depends on the magnitude of the applied magnetic field, which rarely happens for materials with phase transitions of the second order. It has been shown from evaluation of the Temperature averaged Entropy Change (TEC) that a wide temperature range of MCE does not satisfies the requirements of using the compounds studied as an effective magnetocaloric material for magnetic refrigeration. The substitutions in cation sublattices and oxygen non-stoichiometry have negligible effect on TC and magnetocaloric effect (MCE). To investigate the magnetic interactions responsible for the magnetic transitions, the analysis was done by using the modified Arrott plot (MAP) method. The obtained values of the critical exponents matched well with those predicted for the isotropic short range 3D-Heisenberg model.

Comparative phase transformation and magnetocaloric effect study of Co and Mn substitution by Cu in MnCoGe compounds

Structural and magnetic phase transformations and magnetocaloric effect of Mn and Co substitutions by Cu in MnCoGe have been investigated using X-ray diffraction, differential scanning calorimetry, and magnetization measurements. Increase in Cu concentration reduces the martensitic structural and magnetic phase transition temperatures. However, nearly doubling of the amount of Co substitution is required compared to Mn for an equivalent change in the structural transition temperature. A giant magnetocaloric effect, -ΔSMmax ≈ 50 J kg−1K−1 for Δμ0H = 5 T, resulting from coupling of concomitant structural and magnetic transformations near room temperature has been obtained for a sample with around 11 at% Mn-substitution. Fine tuning of Cu concentration (20 at%) in the case of Co substitution resulted in concurrent structural and magnetic transitions at around 260 K. However, the absence of a magnetostructural coupling resulted in peak entropy change of less than 4 J kg−1K−1. Samples with 15 at% or higher Co-substitution showed complex magnetic behavior and multiple magnetic transitions. The nature of magnetic phase transitions in both Co- and Mn-substituted samples have been investigated and phase diagrams for both sets of samples have been derived based on calorimetry and magnetometry results.

Origin of extremely large magnetoresistance in the candidate type-II Weyl semimetal MoTe2\u2212x

The recent observation of extremely large magnetoresistance (MR) in the transition-metal dichalcogenide MoTe2 has attracted considerable interest due to its potential technological applications as well as its relationship with novel electronic states predicted for a candidate type-II Weyl semimetal. In order to understand the origin of the MR, the electronic structure of MoTe2−x (x = 0.08) is systematically tuned by application of pressure and probed via its Hall and longitudinal conductivities. With increasing pressure, a monoclinic-to-orthorhombic (1 T′ to Td) structural phase transition temperature (T*) gradually decreases from 210 K at 1 bar to 58 K at 1.1 GPa, and there is no anomaly associated with the phase transition at 1.4 GPa, indicating that a T = 0 K quantum phase transition occurs at a critical pressure (Pc) between 1.1 and 1.4 GPa. The large MR observed at 1 bar is suppressed with increasing pressure and is almost saturated at 100% for P > Pc. The dependence on magnetic field of the Hall and longitudinal conductivities of MoTe2−x shows that a pair of electron and hole bands are important in the low-pressure Td phase, while another pair of electron and hole bands are additionally required in the high-pressure 1 T′ phase. The MR peaks at a characteristic hole-to-electron concentration ratio (nc) and is sharply suppressed when the ratio deviates from nc within the Td phase. These results establish the comprehensive temperature-pressure phase diagram of MoTe2−x and underscore that its MR originates from balanced electron-hole carrier concentrations.

Aging Behavior and Electric Field Induced Instabilities in Lead Magnesium Niobate - Titanate Relaxor Ferroelectric Single Crystal

The aging characteristics and influence of electric field poling on the phase transitions in (1-x)Pb (Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) [110]-oriented single crystal were examined through temperature dependent complex capacitance study. In addition to two phase transition anomalies exhibited by the crystal in the virgin state, other phase transition instabilities were observed in the complex capacitance of the crystal under the external applied electric field. The aging behavior deviated from the linear logarithmic law and followed the stretched exponential expression typical for relaxor ferroelectrics. Moreover, aging decreased with frequency while it became faster with increase in temperature towards the paraelectric – ferroelectric structural phase transition temperature.

Dynamic signature of orbital selective Mott transition in the metallic phase of VO2

An orbital-selective technique, nuclear magnetic resonance (NMR) spectroscopy, which could simultaneously probe the atomic structure and electronic properties, was employed to address the ‘bad metal’ behaviors, i.e., negligible electron thermal conductivity in the metallic phase of VO2. The measured electric field gradients at V sites by 51V NMR were found to evolve significantly in the pure metallic phase within the vicinity of structural phase transition temperatures, unexpected in a simple metal within this temperature region according to structural analysis by diffraction. This abnormal temperature-dependent local symmetry evolution can be well explained by a simple phenomenological model of orbital selective Mott transition in this multiorbital system.

Structural Phase Transition: Interfacial‐Field‐Induced Increase of the Structural Phase Transition Temperature in Organic–Inorganic Perovskite Crystals Coated with ZnO Nanoshell (Adv. Mater. Interfaces 14/2018)

Structural Phase Transition: Interfacial‐Field‐Induced Increase of the Structural Phase Transition Temperature in Organic–Inorganic Perovskite Crystals Coated with ZnO Nanoshell (Adv. Mater. Interfaces 14/2018)

Structural phase transition, precursory electronic anomaly, and strong-coupling superconductivity in quasi-skutterudite (Sr1−xCax)3Ir4Sn13 and Ca3Rh4Sn13**Project supported by the National Natural Science Foundation of China (Grant Nos. 11674377 and 11634015), the National Key R&D Program of China (Grant Nos. 2017YFA0302904 and 2016YFA0300502), and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB07020200). J. Y. is supported

The interplay between superconductivity and structural phase transition has attracted enormous interest in recent years. For example, in Fe-pnictide high temperature superconductors, quantum fluctuations in association with structural phase transition have been proposed to lead to many novel physical properties and even the superconductivity itself. Here we report a finding that the quasi-skutterudite superconductors (Sr1−xCax)3Ir4Sn13 (x = 0, 0.5, 1) and Ca3Rh4Sn13 show some unusual properties similar to the Fe-pnictides, through 119Sn nuclear magnetic resonance (NMR) measurements. In (Sr1−xCax)3Ir4Sn13, the NMR linewidth increases below a temperature T* that is higher than the structural phase transition temperature Ts. The spin-lattice relaxation rate (1/T1) divided by temperature (T), 1/T1T and the Knight shift K increase with decreasing T down to T*, but start to decrease below T*, and followed by more distinct changes at Ts. In contrast, none of the anomalies is observed in Ca3Rh4Sn13 that does not undergo a structural phase transition. The precursory phenomenon above the structural phase transition resembles that occurring in Fe-pnictides. In the superconducting state of Ca3Ir4Sn13, 1/T1 decays as exp(−Δ/kBT) with a large gap Δ = 2.21kBTc, yet without a Hebel–Slichter coherence peak, which indicates strong-coupling superconductivity. Our results provide new insight into the relationship between superconductivity and the electronic-structure change associated with structural phase transition.

Interfacial‐Field‐Induced Increase of the Structural Phase Transition Temperature in Organic–Inorganic Perovskite Crystals Coated with ZnO Nanoshell

AbstractThe hybrid organic–inorganic perovskites are known to exhibit a complex crystalline structure, which allows for the structural phase transitions among the orthorhombic, tetragonal, and cubic phases that occur at different temperatures. This behavior of the organic–inorganic perovskites can significantly alter their optoelectronic properties. Here, using photoluminescence spectroscopy, it is shown that the structural orthorhombic‐to‐tetragonal phase transition temperature in MAPbI3 perovskite crystal can be increased from 135 to 160 K upon coating with ZnO nanoshell. The phenomenon is attributed to the interfacial‐field‐induced atomic rearrangement in the near‐surface area. The findings shed light on the great importance of the interfacial electric field effect on the structural and optical properties of the organic–inorganic perovskites, which hold great promise for their potential applications in the structural‐phase‐controlled optoelectronic and photovoltaic devices.

Evidence for existence of functional monoclinic phase in sodium niobate based solid solution by powder neutron diffraction

We have carried out systematic temperature-dependent neutron diffraction measurements in conjunction with dielectric spectroscopy from 6 to 300 K for sodium niobate based compounds (1-x) NaNbO3-xBaTiO3 (NNBTx). The dielectric constant is measured as a function of both temperature and frequency. It shows an anomaly at different temperatures in cooling and heating cycles and exhibits a large thermal hysteresis of ∼150 K for the composition x = 0.03. The dielectric constant is found to be dispersive in nature and suggests a relaxor ferroelectric behavior. In order to explore structural changes as a function of temperature, we analyzed the powder neutron diffraction data for the compositions x = 0.03 and 0.05. Drastic changes are observed in the powder profiles near 2θ ∼ 30.6°, 32.1°, and 34.6° in the diffraction pattern below 200 K during cooling and above 190 K in heating cycles, respectively. The disappearance of superlattice reflection and splitting in main perovskite peaks provide a signature for structural phase transition. We observed stabilization of a monoclinic phase (Cc) at low temperature. This monoclinic phase is believed to provide a flexible polarization rotation and considered to be directly linked to the high performance piezoelectricity in materials. The thermal hysteresis for composition x = 0.03 is larger than that for x = 0.05. This suggests that the addition of BaTiO3 to NaNbO3 suppresses the thermal hysteresis. It is also observed that the structural phase transition temperature decreases upon increasing the dopant concentration.

Manifestation of magnetoelastic interactions in Raman spectra of HoxNd1−xFe3(BO3)4 crystals

Raman spectra of Ho[Formula: see text]NdxFe(BO3)4 ([Formula: see text], 0.75, 0.5, 0.25) have been studied in temperature range 10–400[Formula: see text]K. Two compositions ([Formula: see text], [Formula: see text]) demonstrate structural phase transition with soft mode restoration. The addition of Nd atoms increases interatomic spacing and decreases the temperature of structural phase transition. The solid solutions ([Formula: see text], 0.5, 0.25) demonstrate the emergence of the peaks corresponding to magnetoelastic interaction below Néel temperature. The order parameter of the magnetic phase transition has been determined. The equal concentrations of holmium and neodymium atoms prevent magnon soft modes condensation caused by exchange interactions in Fe–O–Fe chains are observed. Calculations confirm the data obtained in the experiment.

Nonlinear Dielectric Response of Nanocomposites Based on Potassium Dihydrogen Phosphate

Nonlinear properties of nanocomposites based on KH2PO4 embedded in nanosized silica matrices with pore sizes of 2.6 and 3.8 nm were investigated. It was found that the structural phase transition temperature for KH2PO4 nanoparticles was higher than that for bulk KH2PO4. Investigations of temperature dependence of the second ( $$\upchi_{2}^{\prime }$$ )- and third ( $$\upchi_{3}^{\prime }$$ )-order dielectric susceptibilities showed the presence of nonlinear properties in the paraelectric phase for the bulk and nanocomposite samples.

Internal friction in particulate composites of (x)Mn0.4Zn0.6Fe2O4 –(1-x)PbZr0.53Ti0.47O3 in the vicinity of the structural phase transition temperatures

The internal friction in particulate ceramic composites of (x)Mn0.4Zn0.6Fe2O4 –(1-x)PbZr0.53Ti0.47O3 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.6) in the vicinity of the phase transition temperatures was studied. We observed the influence of the composite composition on the exponent that characterizes a temperature dependence of the internal friction near the ferroelectric Curie point. The reason for this influence is shown to be the doping of the PbZr0.53Ti0.47O3 ferroelectric phase with atoms of the Mn04Zn0.6Fe2O4 ferrite phase that occurs during high- temperature sintering of composite samples.

Investigation of structural and magnetic properties of Al and Cu doped MnBi alloy

Alloys of Mn-Bi, MnBi-Al and MnBi-Cu were prepared by arc-melting followed by homogenization treatment. All the alloys exhibited hexagonal NiAs crystal structure. Weight fraction of the Low Temperature Phase (LTP) MnBi phase in the Mn-Bi alloy was found to be 88% with a magnetization of 51 emu/gm at 20 kOe, whereas Al and Cu doping resulted in the decrease of the weight fraction of the LTP MnBi phase as well as saturation magnetization. The coercivity is found to increase with the increase in the doping concentration. Upon ball milling the alloys, phase decomposition and a decrease in the magnetization were observed in undoped Mn-Bi alloy. On the other hand, there was no significant phase decomposition and change in the magnetization in doped MnBi alloys due to ball milling. A change in the magneto structural phase transition temperature of MnBi was observed with doping, which is attributed to the lattice modifications occurring in the MnBi system. Doped and undoped Mn-Bi alloys shows increase in coercivity with temperature. Details of investigation are presented in this paper.

Hidden phase in parent Fe-pnictide superconductors

We investigate the origin of exoticity in Fe-based systems via studying the Fermiology of CaFe2As2 employing Angle Resolved Photoemission spectroscopy (ARPES). While the Fermi surfaces (FSs) at 200 K and 31 K are observed to exhibit two dimensional (2D) and three dimensional (3D) topology, respectively, the FSs at intermediate temperatures reveal emergence of the 3D topology at much lower temperature than the structural & magnetic phase transition temperature (170 K, for the sample under scrutiny). This leads to the conclusion that the evolution of FS topology is not directly driven by the structural transition. In addition, we discover the existence in ambient conditions of energy bands related to the collapsed tetragonal (cT) phase. These bands are distinctly resolved in the high-photon energy spectra exhibiting strong Fe 3d character. They gradually move to higher binding energies due to thermal compression with cooling, leading to the emergence of 3D topology in the Fermi surface. These results reveal the so-far hidden existence of a cT phase in ambient conditions, which is argued to lead to quantum fluctuations responsible for the exotic electronic properties in Fe-pnictide superconductors.

Фотопроводимость неводных липосом: новый метод измерения температур структурных фазовых переходов фосфолипидных мембран

Фотопроводимость неводных липосом: новый метод измерения температур структурных фазовых переходов фосфолипидных мембран

Microwave absorption through the martensitic and Curie transitions in Ni45Cr5Mn37In13

We have investigated the electron spin resonance (ESR) of the Ni45Cr5Mn37In13 Heusler alloy near the structural and magnetic phase transition temperatures. Ni45Cr5Mn37In13 is characterized by a first order magnetostructural (martensitic) transition (MST) with magneto-responsive properties such as magnetoresistance, Hall and magnetocaloric effects, etc., in the vicinity of the MST. Since the details and origins of these behaviors are not well understood, we used a technique beyond magnetometry, i.e., “microwave absorption”, to reveal new information. ESR studies of Ni45Cr5Mn37In13 shows that this compound is characterized by wide absorption spectra at temperatures greater than 250 K that depend on the angle of the magnetic field relative to the normal to the sample plate (α) and temperature (T). Two local maxima at about 5 and 6 kOe were detected for α close to zero degrees near the martensitic transition and Curie temperatures. The absorption spectra are discussed along with the results of the structural and magnetic studies.

Investigation of phase evolution and control over phase transformation temperature and thermal hysteresis using stoichiometry and co-doping in VO2 thin films

Structural phase transition temperature and its associated hysteresis in VO2 have been controlled by high valent dopant induced local structural modification which acts as phase nucleation site during phase transformation. Monoclinic phase intensity loops plotted against temperature has been observed to exhibit thermal hysteresis. It is shown that the size, shape and central position of hysteresis loop depend on stoichiometry and doping concentration. Highest reduction in phase transformation temperature and thermal hysteresis width has been observed in case of W+6-Mo+6 co-doping and W+6 doping, respectively. Hence energy barrier associated with the structural phase transition has been successfully manipulated to vary Tc and hysteresis width. These findings have implications for designing the phase switching devices and smart window applications.