Search results for "Hysteresi"
showing 10 items of 250 documents
Pressure Tunable Electronic Bistability in Fe(II) Hofmann-like Two-Dimensional Coordination Polymer [Fe(Fpz)2Pt(CN)4]: A Comprehensive Experimental a…
2021
A comprehensive experimental and theoretical study of both thermal-induced spin transition (TIST) as a function of pressure and pressure-induced spin transition (PIST) at room temperature for the two-dimensional Hofmann-like SCO polymer [Fe(Fpz)2Pt(CN)4] is reported. The TIST studies at different fixed pressures have been carried out by magnetic susceptibility measurements, while PIST studies have been performed by means of powder X-ray diffraction, Raman, and visible spectroscopies. A combination of the theory of elastic interactions and numerical Monte Carlo simulations has been used for the analysis of the cooperative interactions in TIST and PIST studies. A complete (T, P) phase diagram…
Bidirectional photo-switching of the spin state of iron(II) ions in a triazol based spin crossover complex within the thermal hysteresis loop
2009
Abstract We have investigated the effect of short laser pulses (532 nm, 4 ns, −2 ) on the spin state of iron(II) ions in the spin crossover compound {[Fe II (Htrz) 2 (trz)](BF 4 )} within the hysteresis region of the high-spin (HS) to low-spin (LS) first-order thermal phase transition. Using Raman spectroscopy we have evidenced quasi-complete HS → LS as well as LS → HS photo-conversions, which can be induced by a single laser shot in the descending (351 K) and ascending (378 K) branches of the hysteresis loop, respectively. No effect has been observed, however, close to the center of the hysteresis loop even for repeated exposures.
Analytical solution of 1D Ising-like systems modified by weak long range interaction
1999
It is well-known that 1D systems with only nearest neighbour interaction exhibit no phase transition. It is shown that the presence of a small long range interaction treated by the mean field approximation in addition to strong nearest neighbour interaction gives rise to hysteresis curves of large width. This situation is believed to exist in spin crossover systems where by the deformation of the spin changing molecules, an elastic coupling leads to a long range interaction, and strong bonding between the molecules in a chain compound leads to large values for nearest neighbour interaction constants. For this interaction scheme an analytical solution has been derived and the interplay betwe…
The structural and dielectric properties of the Na0.96Li0.04NbO3ceramics
2007
Ceramic samples Na0.96Li0.04NbO3 were obtained using ceramic technology. The phase and structural analysis, the microstructure, EDS and EPMA, dielectric and hysteresis loops measurements have been performed. The dielectric and hysteresis loops measurements of Na0.96Li0.04NbO3 have been carried out. The dielectric measurements were performed both without and under axial pressure up to 120 MPa. It was shown that Na0.96Li0.04NbO3 ceramics have orthorhombic symmetry at room temperature and undergo a first order phase transition at a temperature of about 570 K. The axial pressure shifts the phase transition temperature and decreases the hysteresis in field-polarisation and field-strain dependenc…
Dielectric polarization in PLZT X/65/35 and PbMg1/3Nb2/3O3at the diffuse phase transition
1992
Abstract The transformation of the hysteresis loops in PLZT x/65/35 in the region of diffuse phase transition is discussed in relation to the behaviour of dielectric permittivity. The Vogel-Fulcher type dielectric relaxation is used to describe the discussed phenomena.
Physical properties of ferroelectric film with continuous space charge distribution
2014
We present a theory of ferroelectric phase transitions in a film with a homogeneously distributed space charge leading to the so-called built-in polarization. On the base of our complete solution of the problem of continuous space charge distribution in a ferroelectric film, we calculate the ferroelectric phase transition temperature , spatial polarization distribution in paraelectric and ferroelectric phases as well as hysteresis loop in the ferroelectric phase. We have shown that the presence of continuous space charge in a film inhibits the ferroelectricity in it: it lowers the ferroelectric phase transition temperature and coercive field. Our estimates of these differences show that the…
Study of charge density waves in suspended 2H-TaS 2 and 2H-TaSe 2 by nanomechanical resonance
2021
The charge density wave (CDW) state in van der Waals systems shows interesting scaling phenomena as the number of layers can significantly affect the CDW transition temperature, $T_{CDW}$. However, it is often difficult to use conventional methods to study the phase transition in these systems due to their small size and sensitivity to degradation. Degradation is an important parameter which has been shown to greatly influence the superconductivity in layered systems. Since the CDW state competes with the onset of superconductivity, it is expected that $T_{CDW}$ will also be affected by the degradation. Here, we probe the CDW phase transition by the mechanical resonances of suspended 2H-TaS…
The impact of thermophysical properties and hysteresis effects on the energy performance simulation of PCM wallboards: Experimental studies, modellin…
2020
Abstract This paper presents a combined experimental and numerical procedure, developed to test the thermophysical behaviour of a real scale PCM wallboard, aiming at providing reliable data for the validation of building energy performance simulation tools. Data obtained from two experimental tests, conducted on real building elements integrating PCM undergoing complete and incomplete phase change, are considered for assessing the impact of thermal properties and hysteresis. A comprehensive comparative numerical analysis, performed by means of an in-house developed simulation tool, called DETECt, is carried out to investigate the reliability of several modelling and simulation approaches av…
Phase Transitions in Li, K and Ag Modified Na1/2Bi1/2TiO3-SrTiO3-PbTiO3Solid Solutions
2012
Influence of moderate substitution of Na by monovalent metals Li, K and Ag on structure, phase transitions and dielectric properties of 0.4Na1/2Bi1/2TiO3-0.4SrTiO3-0.2PbTiO3 is studied. Substitution by Li increases, while substitution by K and Ag decreases tetragonality of unit cell. Li increases, Ag decreases while K weakly influences phase transition temperature. The characteristic for the parent phase relaxor state with Tt approaching Tm in case of substitution by K and Li transfers into diffused phase transition without Tm dependence on frequency and extended region of thermal hysteresis.
Meltable Spin Transition Molecular Materials with Tunable Tc and Hysteresis Loop Width.
2015
Herein, we report a way to achieve abrupt high-spin to low-spin transition with controllable transition temperature and hysteresis width, relying not on solid-state cooperative interactions, but utilizing coherency between phase and spin transitions in neutral FeII meltable complexes