Search results for "Ferro"
showing 10 items of 2451 documents
Crystal growth and hysteresis phenomena of rubidium tetrachlorozincate Rb2ZnCl4
1988
Abstract Phase transitions in Rb2ZnCl4 crystals grown by various methods are examined with differential scanning calorimetry and dielectric measurements. For most of the studied samples the permittivity along the ferroelectric axis shows a large thermal hysteresis over a wide temperature range including the incommensurate phase and the lock-in point. This hysteresis depends on the presence of different defects which appear during crystal growth or after a thermal and mechanical treatment. It is shown that dielectric measurements are quite well suited to characterize the crystals exhibiting on incommensurate phase and a ferroelectric phase.
Ferroelectric Properties and Crystal Structure of YBa2Cu3O7/BaxSr(1−x)TiO3 Heterostructures
1997
ABSTRACTEpitaxial YBa2Cu3O7/Ba0.5Sr0.5TiO3 (YBCO/BST) and YBCO/BaTiO3 (BTO) heterostructures were prepared by dc and rf sputtering on SrTiO3 and MgO substrates. The YBCO/BTO bilayers exhibit an inductive superconducting transition temperature of 85 K and the ferroelectric phase transition of BST shows a Curie-Weiss temperature of 310 K. Microstructure was investigated by x-ray-diffraction and atomic force microscopy. In this work we also studied the insulator's conductivity and the contribution of domain walls to permittivity.
Sb Effect on Structural, Dielectric, and Ferroelectric Properties of Na0.5K0.5NbO3Ceramics
2015
Lead-free Na0.5K0.5(Nb1-xSbx)O3 (0<x<0.05) ceramics were fabricated by the solid-state reaction method and materials with more than 95% densification were obtained. A microstructure study confirms that the ceramics are well sintered. All compositions show complete perovskite solid solutions. Structural, dielectric and ferroelectric investigations for these specimens were performed. X-ray measurements showed that all compositions have a single perovskite structure with orthorhombic symmetry. Dielectric study revealed that the ceramics obtained are normal ferroelectrics. However some signs of diffuse phase transition were observed. The transition temperatures and the maximum electric permitti…
Uniaxial stress dependence of the dielectric and ferroelectric properties of the Na0.5K0.5NbO3and Na0.5K0.5NbO3 + 0.5 mol%MnO2ceramics
2013
Na0.5K0.5NbO3 and Na0.5K0.5NbO3 + 0.5 mol%MnO2 lead-free ceramics have been produced by solid phase hot pressing sintering process at 1120–1145°C. The results of the X-ray diffraction measurements showed that the obtained samples possessed a perovskite structure. The micrograph of the fractured surface showed a dense ceramic structure, in compliance with 93% relative density determined by the Archimedes method. The dependence of dielectric and ferroelectric properties on the uniaxial compressive stress (0–3000 bar) of the Na0.5K0.5NbO3 and Na0.5K0.5NbO3 + 0.5 mol%MnO2 ceramics was investigated. Significant influence of the external stress on these properties was revealed. It includes a shif…
Bias Field Effect on Dielectric Response in the Region of Phase Transitions in (Pb,La)(Zr,Sn,Ti)O3Ceramics
2007
The dielectric response of (Pb 0.97 La 0.02 ) (Zr 0.53 Ti 0.12 Sn 0.35 )O 3 (PLZTS-2/53/12/35) ceramics was measured as a function of DC bias field E =. As the bias field intensity increases the values of ϵ′ max and ϵ” max are found to shift towards a lower temperature. A possible coexistence of the ferroelectric and antiferroelectric phases over a wide range of temperatures in the PLZTS-2/53/12/35 samples is assumed to explain the observed features of ϵ′ (T), ϵ” (T), and ϵ′ (E=) curves.
Influence of Compressive Stress on Dielectric and Ferroelectric Properties of the Na0. 5K0.5NbO3, Na0.5K0.5(Nb0.94Sb0.06)O3and Na0.5K0.5(Nb0.94Sb0.06…
2013
Good quality lead-free ceramics of Na0.5K0.5NbO3, Na0.5K0.5(Nb0.94Sb0.06)O3 and Na0.5K0.5(Nb0.94Sb0.06)O3 +0.5mol%MnO2 have been produced by a solid phase hot pressing sintering process at 1120–1145°C. The dependence of dielectric and ferroelectric properties on the uniaxial pressure (0–3000 bar) of the these samples was investigated, revealing a significant influence of the external stress on their properties. This includes a shift of the phase transition, a diffuseness of the permittivity characteristics, a change of the dielectric dispersion and a decrease of the polarization. We discuss our results based on hardening of the soft-mode and domain switching processes under applying of pres…
Low frequency nonlinearity in layered ferroelectrics BaBi<inf>2</inf>Nb<inf>2</inf>O<inf>9</inf> and SrBi<inf&…
2010
The dielectric nonlinearity in layered ferroelectric ceramics of BaBi 2 Nb 2 O 9 and SrBi 2 Ta 2 O 9 is studied by analysing polarisation loops and measuring dielectric permittivity as a function of frequency. In case of BaBi 2 Nb 2 O 9 the system has a broad phase transition manifesting essential features of a slow relaxation of polarisation; in case of SrBi 2 Ta 2 O 9 the processes contributing to polarisation switching are driven by rearrangement of the domain structure.
Structure, ferroelasticity and Goldilocks zone phase transitions in C3H5N2Al(SO4)2·6H2O
2021
The single crystal growth and sequence of reversible phase transition are described for C3H5N2Al(SO4)2·6H2O. Thermal and structural analyses combined with dielectric studies and optical observations revealed the structural phase transition at T 1 = 339/340 K (I↔II) and T 2 = 347/348 K (II↔III) on heating and cooling, respectively. Both phase transitions are of the first-order type. The symmetry changes from monoclinic to trigonal phase. At 293 K, the large crystals are usually divided into numerous domains of the ferroelastic type that disappear above T 1 on heating and reappear below T 1 on cooling. The domain structure pattern is characteristic for the transition between trigonal and mono…
Terahertz conductivity of the heavy-fermion compound UNi2Al3
2011
We have studied the optical properties of the heavy-fermion compound UNi${}_{2}$Al${}_{3}$ at frequencies between 100 GHz and 1 THz (3 and 35 cm${}^{\ensuremath{-}1}$), temperatures between 2 and 300 K, and magnetic fields up to 7 T. From the measured transmission and phase shift of radiation passing through a thin film of UNi${}_{2}$Al${}_{3}$, we have directly determined the frequency dependence of the real and imaginary parts of the optical conductivity (or permittivity, respectively). At low temperatures the anisotropy of the optical conductivity along the $a$ and $c$ axes is about 1.5. The frequency dependence of the real part of the optical conductivity shows a maximum at low temperat…
The physical mechanisms of relaxation times distribution in inorganic and organic disordered ferroelectrics
2007
Abstract We discuss the physical background for relaxation times distribution in organic and inorganic disordered ferroelectrics. We show that such background is a disorder which is believed to be a reason for relaxor behavior. Due to this disorder the internal electric and elastic fields are of a random nature being characterized by certain distribution function. Having the distribution function f ( E ) of random field E , we can obtain the distribution function of relaxation times F ( τ ) with the help of relation between τ and E . Latter relation can be obtained considering the dynamics of a single electric dipole in a random field created by the ensemble of defects and impurities in a s…