Search results for "Phase Transition"
showing 10 items of 1281 documents
LEAD-FREE (Na0.5Bi0.5)1-xBaxTiO3 SINGLE CRYSTALS (0 ≤ x ≤ 0.05) AND THEIR DIELECTRIC AND PYROELECTRIC PROPERTIES
2009
ABSTRACT Lead-free single crystals of Na0.5Bi0.5TiO3-BaTiO3 (NBT-BT) system were prepared by Czochralski method and their dielectric and pyroelectric properties have been studied. The results were compared with these for pure NBT. The obtained samples show pure perovskite structure with rhombohedral symmetry at room temperature. Low frequency (100 Hz–100 kHz) investigations reveal the diffuse phase transitions. The obtained results are discussed in terms of local electric and strain fields caused by different ionic radius of (Na, Bi) and Ba ions. The NBT-BT system is expected to be a new promising candidate for lead-free electronic crystals.
EoP250. Recent advances in transparent ferroelectric ceramics research and applications
1992
Abstract The studies of field-induced lattice rearrangement and field-induced phase transition (PT), laser beam effects in transparent ferroelectric ceramics (TFC), dopant and radiation effects in PLZT, Kerr effect demonstration and application of an intracavity matrix-addressed spatial-time modulator are discussed.
A thermotropic liquid crystal elastomer micro-actuator with integrated deformable micro-heater
2014
We present a liquid crystal elastomer (LCE) actuator with large stroke and fast reaction time. LCEs show a large macroscopic shape change when heated above the phase transition (≈120°C). Buried wafer-level fabricated micro-heaters offer optimal thermal reaction times and compact design of the actuators. A relative length change of λ = 1.28 was obtained with 320 mW power consumption. Heating the device from room temperature takes τrise = 19.7 s, cooling below the phase transition temperature from the fully contracted state needs τfall - 5.6s. We verify that the displacement may be accurately controlled by varying electrical input power.
Bioinspired actuated adhesive patterns of liquid crystalline elastomers.
2012
Gecko-inspired arrays of micropillars made of a liquid crystalline elastomer display thermoswitchable adhesive behavior as a consequence of elongation changes caused by reorientation of the mesogens at the nematic-isotropic (N-I) phase transition.
Phase transitions and upconversion luminescence in oxyfluoride glass ceramics containing Ba4Gd3F17 nanocrystals
2017
This is the peer reviewed version of the following article: G. Krieke, A. Sarakovskis, R. Ignatans, J. Gabrusenoks "Phase transitions and upconversion luminescence in oxyfluoride glass ceramics containing Ba4Gd3F17 nanocrystals", Journal of the European Ceramic Society, 2017, 37 (4), which has been published in final form at https://www.sciencedirect.com/science/article/abs/pii/S0955221916306768 This article may be used for non-commercial purposes in accordance with Elsevier Terms and Conditions for Sharing and Self-Archiving.
Pressure-induced structural evaluation and insulator-metal transition in the mixed spinel ferrite Zn0.2Mg0.8Fe2O4
2017
The effect of pressure on the electronic properties and crystal structure in a mixed spinel ferrite $\mathrm{Z}{\mathrm{n}}_{0.2}\mathrm{M}{\mathrm{g}}_{0.8}\mathrm{F}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ was studied for the first time up to 48 GPa at room temperature using x-ray diffraction, Raman spectroscopy, and electrical transport measurements. The sample was cubic (spinel-type $Fd\overline{3}m$) at ambient pressure and underwent a pressure-induced structural transition to an orthorhombic phase $(\mathrm{CaT}{\mathrm{i}}_{2}{\mathrm{O}}_{4}\ensuremath{-}\mathrm{type}\phantom{\rule{0.16em}{0ex}}Bbmm)$ at 21 GPa. This structural transformation corresponded to a first-order phase transition …
Electronic structure of the austenitic and martensitic state of magnetocaloric Ni-Mn-In Heusler alloy films
2013
Changes of the electronic and magnetic structure near the martensitic phase transition of Ni-Mn-In Heusler alloys doped with Co are investigated by experiment and theory. The nonstoichiometric Ni${}_{48}$Co${}_{5}$Mn${}_{35}$In${}_{12}$ epitaxial film undergoes a transition from a weakly magnetic martensitic phase below ${T}_{m}=350$ K to a ferromagnetic austenitic phase above ${T}_{m}$. Element-specific magnetic moments and the unoccupied density of states function is investigated using x-ray magnetic circular dichroism. We find an antiparallel alignment of Mn and Ni/Co magnetic moments in both phases. The electronic structure is calculated using the SPR-KKR Green's function approach consi…
Magnetotransport Properties of Thin Films of Magnetic Perovskites
2007
In this article we show magnetotransport of two prototypical (nearly) half metallic perowskites La2/3Ca1/3MnO3 and Sr2FeMoO6. In a half metal the spin polarisation at the Fermi energy is complete and tunneling magnetoresistive devices of high sensitivity can be realized with small external magnetic fields. In the vicinity of the metal-insulator phase transition (MIT) temperature of the manganite an external magnetic field can induce ’colossal’ magnetoresistive effects. In the simple perovskites La1-x Ca x MnO3 the charge transport above the MIT is of polaronic nature. Hall-effect measurements on the compound La0.67Ca0.33MnO3 below the MIT show a compensated Fermi-surface consisting of elect…
Anisotropies and magnetic phase transitions in insulating antiferromagnets determined by a Spin-Hall magnetoresistance probe
2019
Antiferromagnets possess a number of intriguing and promising properties for electronic devices, which include a vanishing net magnetic moment and thus insensitivity to large magnetic fields and characteristic terahertz frequency dynamics. However, probing the antiferromagnetic ordering is challenging without synchrotron-based facilities. Here, we determine the material parameters of the insulating iron oxide hematite, α-Fe2O3, using the surface sensitive spin-Hall magnetoresistance (SMR). Combined with a simple analytical model, we extract the antiferromagnetic anisotropies and the bulk Dzyaloshinskii-Moriya field over a wide range of temperatures and magnetic fields. Across the Morin phas…
Ferroelastic phase transitions of alkali halide-alkali cyanide mixed crystals
1990
Abstract The alkali cyanides and their CN-rich mixtures with alkali halides are proper ferroelastics with transitions from the cubic high temperature phase into the various non-cubic low temperature phases. As the CN concentration is reduced, the transformations temperature decreases and eventually the ferroelastic low temperature state is suppresse in favour of a glass-like state. The structural and elastic properties of these compounds are discussed with a special emphasis on the martensitic aspect of the transitions.