- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Additional phase transition in a PbZr <sub/>0.87</sub> Ti <sub/>0.13</sub> O <sub/>3</sub> single crystal
摘要： PbZr1-xTixO3 (PZT) ceramics are one of the most known and widely used piezoelectric materials. In order to understand the origin of the high piezoelectricity it is essential to also understand its phase diagram. Many recent papers reported on the modification of PZT phase diagram based on ceramic experimental data. This is due to difficulties to get good quality single crystal samples. We have succeeded in getting a good quality single crystal with x= 0.13. Based on temperature changes of elastic properties we confirmed the existence of additional phase transition appearing in the PbZr0.87Ti0.13O3. The temperature dependence of the elastic properties was investigated by means of piezoelectric measurements and Brillouin light scattering. We discussed the correlation between anomalies of the elastic properties found in these measurements, and suggested that, except for the two well-known phase transitions, these anomalies point to another phase transition below Tc. The structure and symmetry of this crystal have been tested with use of the x-ray diffraction at the room temperature.
关键词： x-ray diffraction,phase transitions,elastic properties,piezoelectricity,PZT single crystals
更新于2025-09-23 15:22:29
-
Persistence of the R3m Phase in Powder GeTe at High Pressure and High Temperature
摘要： As a phase-change material, rhombohedral GeTe (space group R3m) was believed to transform to the cubic rock-salt phase (B1) at 3–4 GPa, associated with the disappearance of a Peierls distortion. However, using a combination of synchrotron X-ray diffraction and theoretical calculations, we found that the R3m phase persists from ambient pressure up to pressures of about 15.8 GPa, in contrast to previous reports. Neither was the B1 phase observed in a heating X-ray powder diffraction experiment. The spurious transformation from R3m to B1 is caused by changes to the compression ratio of lattice parameters in the R3m phase under high pressure/temperature. These findings provide insight into transitions of phase-change materials, relevant to other materials undergoing displacive transitions under high pressure/temperature.
关键词： structural phase transitions,density-functional theory,high pressure,phase-change materials,high temperature,GeTe,synchrotron X-ray diffraction
更新于2025-09-23 15:21:01
-
Raman high-pressure study of butane isomers up to 40 GPa
摘要： Raman spectroscopy studies on n and i-butane were performed at pressures of up to 40 GPa at ambient temperatures using the DAC technique. Normal butane undergoes two phase transitions at 1.9(5) GPa and 2.9(5) GPa and isobutane at 2.7(5) GPa and 3.5(5) GPa. These phase transitions were identi?ed based on observations of the splitting Raman modes and the appearance or disappearance of particular Raman peaks. Our results demonstrate the complex, high-pressure behavior of butane isomers.
关键词： Raman spectroscopy,high-pressure,DAC technique,phase transitions,butane isomers
更新于2025-09-23 15:21:01
-
The phase transitions in selective laser-melted 18-NI (300-grade) maraging steel
摘要： Dilatometric studies in 18-Ni steel components fabricated by selective laser melting technique were carried out to determine the influence of heating rate on transitions occurring during the heating cycle. SLM components have been examined in controlled heating and cooling cycles. For analysis, heating of the analysed materials was carried out at heating rates of 10, 15, 20, 30 and 60 °C min?1. During the heating process, two solid-state reactions were identified—i.e. precipitation of intermetallic phases and the reversion of martensite to austenite. A simplified procedure based on the Kissinger equation was used to determine the activation energy of individual reactions. For precipitation of intermetallic phases, the activation energy was estimated 301 kJ mol?1, while the martensite to austenite reversion was determined at the activation energy 478 kJ mol?1.
关键词： Precipitation,Martensite reversion,Phase transitions,Maraging steels
更新于2025-09-23 15:21:01
-
Coexistence of pressure-induced structural phases in bulk black phosphorus: a combined x-ray diffraction and Raman study up to 18 GPa
摘要： We report a study of the structural phase transitions induced by pressure in bulk black phosphorus by using both synchrotron x-ray diffraction for pressures up to 12.2 GPa and Raman spectroscopy up to 18.2 GPa. Very recently black phosphorus attracted large attention because of the unique properties of few-layers samples (phosphorene), but some basic questions are still open in the case of the bulk system. As concerning the presence of a Raman spectrum above 10 GPa, which should not be observed in an elemental simple cubic system, we propose a new explanation by attributing a key role to the non-hydrostatic conditions occurring in Raman experiments. Finally, a combined analysis of Raman and XRD data allowed us to obtain quantitative information on presence and extent of coexistences between different structural phases from ~5 up to ~15 GPa. This information can have an important role in theoretical studies on pressure-induced structural and electronic phase transitions in black phosphorus.
关键词： high pressure,black phosphorus,x-ray diffraction,Raman spectroscopy,phase transitions
更新于2025-09-23 15:21:01
-
Phase transitions in nanofilms of polar smectic liquid crystals with multilayer periodicity
摘要： Optical investigations and calculation of structures were performed on ?lms of liquid crystal with the sequence of phase transitions in the bulk sample SmC??SmC??SmA?I. We investigated freestanding nano?lms with number of smectic layers from 2 to 6 with thickness commensurate, smaller, or greater than the period of SmC?d4 phases of the bulk sample. The number of phase transitions increases as the ?lm thickness increases. Under temperature change the transitions occur with conservation as well as with change of the direction of ?lm polarization with respect to the molecular tilt plane. In thick ?lms at high temperature the ?lm can be switched by electric ?eld from the state with longitudinal (parallel to the molecular tilt plane) into a state with transverse (perpendicular to the molecular tilt plane) electric polarization. In the framework of Landau theory of phase transitions, structures and phase transitions in the bulk sample and in nano?lms were calculated; values of interlayer interactions were estimated. The molecular structure was assumed to be planar with different sequences of synclinic and anticlinic orderings in nearest layers. The results of calculations are in good agreement with experiment.
关键词： multilayer periodicity,Landau theory,phase transitions,nano?lms,polar smectic liquid crystals
更新于2025-09-23 15:21:01
-
Ferroelectric properties and phase transitions of high performance vertically aligned KNN nanowire-arrays grown by pulsed laser deposition
摘要： Pulsed laser deposition (PLD) was used to synthesize piezoelectric nanowire-arrays of K0.5Na0.5NbO3 (KNN) on Pt/TiO2/SiO2/Si substrates. These arrays were successfully prepared by using two different deposition conditions than the previously reported for KNN. KNN with orthorhombic structure and minority secondary phases were identified by XRD. Ferroelectric and Piezoelectric properties were confirmed by piezoresponse force microscopy, and showed that nanowire-arrays have an improvement in their effective piezoelectric coefficient of d33eff = 94.6 pm/V and 133.6 pm/V, higher than previously reported coefficients. Pulsed laser photoacoustic technique was used to analyze the phase transition temperatures and they showed a phase transition (O-T) at ～170 ?C and a phase transition (T-C) at ～360 ?C, lower temperatures than those found for bulk ceramics. Furthermore, it was identified the presence of minor amount of secondary ferroelectric phase (K4Nb6O17).
关键词： Phase transitions,KNN nanowire-arrays,Ferroelectric properties,Pulsed laser deposition,Piezoelectric coefficient
更新于2025-09-23 15:19:57
-
Strongly Enhanced Berry Dipole at Topological Phase Transitions in BiTeI
摘要： Transitions between topologically distinct electronic states have been predicted in different classes of materials and observed in some. A major goal is the identification of measurable properties that directly expose the topological nature of such transitions. Here, we focus on the giant Rashba material bismuth tellurium iodine which exhibits a pressure-driven phase transition between topological and trivial insulators in three dimensions. We demonstrate that this transition, which proceeds through an intermediate Weyl semimetallic state, is accompanied by a giant enhancement of the Berry curvature dipole which can be probed in transport and optoelectronic experiments. From first-principles calculations, we show that the Berry dipole—a vector along the polar axis of this material—has opposite orientations in the trivial and topological insulating phases and peaks at the insulator-to-Weyl critical points, at which the nonlinear Hall conductivity can increase by over 2 orders of magnitude.
关键词： Berry curvature dipole,Weyl semimetallic state,BiTeI,nonlinear Hall conductivity,topological phase transitions
更新于2025-09-23 15:19:57
-
Effect of Sodium and Fluorine Co-Doping on the Properties of Fluorite-Like Rare-Earth Molybdates of Nd5Mo3O16 type
摘要： Fluorite-like oxyfluorides NaLn4Mo3O15F (Ln = La, Pr, Nd), which relate to the Nd5Mo3O16 structural type, were obtained by solid-phase synthesis in the air. Codoping of the Nd5Mo3O16+δ family with sodium and fluorine led to the appearance of a piezoelectric effect and a reversible phase transition in oxyfluorides, accompanied by a jump in the conductivity and an anomaly of the permittivity of the compounds. In contrast to Nd5Mo3O16+δ, which possess mixed oxide-ion/electronic interstitial conductivity, the NaLn4Mo3O15F compounds can have oxygen conductivity of vacancy type. The highest conductivity offered by these materials is 3.2×10–2 S/cm at 700 °C. NaLn4Mo3O15F compounds were found to be hygroscopic and can be considered as potential proton conductors.
关键词： rare earths,sodium,phase transitions,fluorine,solid-phase synthesis
更新于2025-09-19 17:15:36
-
Comparing the anomalous Hall effect and the magneto-optical Kerr effect through antiferromagnetic phase transitions in Mn <sub/>3</sub> Sn
摘要： In the non-collinear antiferromagnet Mn3Sn, we compare simultaneous measurements of the anomalous Hall effect (AHE) and the magneto-optical Kerr effect (MOKE) through two magnetic phase transitions: the high-temperature paramagnetic/antiferromagnetic (AF) phase transition at the N(cid:2)eel temperature (TN (cid:2) 420 K) and a lower-temperature incommensurate magnetic ordering at T1 (cid:2) 270 K. While both the AHE and MOKE are sensitive to the same underlying symmetries of the AF non-collinear spin order, we ?nd that the transition temperatures measured by these two techniques unexpectedly differ by approximately 10 K. Moreover, the applied magnetic ?eld at which the AF order reverses is signi?cantly larger when measured by MOKE than when measured by AHE. These results point to a difference between the bulk and surface magnetic properties of Mn3Sn.
关键词： antiferromagnetic phase transitions,anomalous Hall effect,magneto-optical Kerr effect,Mn3Sn
更新于2025-09-19 17:15:36