Search results for "Transition temperature"
showing 10 items of 137 documents
True Nanoferroics with the Properties Absent in Corresponding Bulk Samples
2013
The Chapter covers the theoretical and experimental approaches to the investigations of the physical properties, which are inherent in ferroics of nanosize and absent in corresponding bulk materials. Namely, the strong surface influence along with other effects of geometrical confinement generates number of physical effects, which do not occur in bulk ferroics samples. One example of such phenomena is room-temperature ferromagnetism in nanoparticles and thin films of undoped CeO2, HfO2, SnO2, Al2O3 and other nonmagnetic (in bulk samples) oxides. Theo other striking example is appearance of so-called spontaneous flexoeffects (i.e. flexoelectric, flexomagnetic, flexoelastic) in ferroic nanosa…
The influence of hydrostatic pressure on hysteresis phase transition in spin crossover compounds
1999
Abstract The effect of hydrostatic pressure on the transition temperature and the hysteresis widths of first order spin crossover phase transitions has been studied. A decrease as well as an increase of the hysteresis width with increasing pressure was reported in the literature. The increase of width with increasing pressure contradicts the expectation derived from mean field theory. We remeasured the pressure dependence of the temperature hysteresis of the compound [Fe(phy)2](BF4)2 (phy=1, 10-phenanthroline-2-carbaldehydephenylhydrazone). The spin transition temperatures at ambient temperature are T ↑ 1/2 =289±1 K, T ↓ 1/2 =283±1 K . An increase of the hysteresis width of d Δ T 1/2 / d p=…
N2monolayers physisorbed on graphite: the herringbone transition revisited
1994
Monte Carlo simulations were undertaken of the orientational herringbone phase transition of N2 adsorbed on graphite in the complete monolayer (✓3 × ✓3) R30° structure. The non-universal aspects (c...
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…
Phase transition of tetragonal copper sulfide Cu2S at low temperatures
2017
The low-temperature behavior of tetragonal copper sulfide, ${\mathrm{Cu}}_{2}\mathrm{S}$, was investigated by powder and single-crystal x-ray diffraction, calorimetry, electrical resistance measurements, and ambient temperature optical absorption spectroscopy. The experiments were complemented by density-functional-theory-based calculations. High-quality, polycrystalline samples and single crystals of tetragonal copper sulfide were synthesized at 5 GPa and 700 K in a large volume multianvil press. Tetragonal ${\mathrm{Cu}}_{2}\mathrm{S}$ undergoes a temperature-induced phase transition to an orthorhombic structure at around 202 K with a hysteresis of $\ifmmode\pm\else\textpm\fi{}21$ K, an e…
Size effects of static and dynamic polarization in ferroelectric thin film multilayers
2001
Abstract A thermodynamic theory for the calculation of static and dynamic polarization profiles of ferroelectric thin film multilayers is developed. The free energy functional is written down using a multilayer model in which c-domain layers of the ferroelectric material alternate with a-domain layers of a second ferroelectric materials. We assume that the interfaces are perfectly sharp and that the polarization at these boundaries is zero. The equilibrium polarization profile, its temperature and thickness dependencies were determined from the solutions of the Euler-Lagrange equations. A thickness induced ferroelectric phase transition is shown to exist and its transition temperature and c…
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…
Dimesogenic ferroelectric polysiloxanes
1994
Dimesogenic polysiloxane [Si(Me) 2 O] m [Si(Me)(R)O] n (R= (CH 2 ) 3 CH(COO[CH 2 ] 11 OPhPhOCOPh(NO 2 )OC * H(Me)C 6 H 13 ) 2 are synthesized by hydrosilylation. The phase transition temperaturs are determined and the ferroelectric properties are investigated
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.
Path-Integral Monte Carlo Simulation for H2 and D2 Adsorbed on Graphite
1997
Molecular layers are very good realizations of two dimensional systems. Hydrogen molecules H 2,HD,D 2 adsorbed on graphite are excellent model systems for investigating the influence of substrate fields and of quantum effects on phase transitions. At a coverage of a complete commensurable layer in the √3 x √3 R30° structure experiments showed an anomalous effect, the system with the lighter H 2 molecules has a higher order-disorder transition temperature compared to the system with the heavier D 2 molecules. By a combination of path integral Monte Carlo and finite size scaling techniques we analyze this effect. In detail we study the order parameter and the cumulants and discuss the impact …