Anomalous Thermal Hysteresis Research Articles

Coexistence of Interacting Charge Density Waves in a Layered Semiconductor.

Coexisting orders are key features of strongly correlated materials and underlie many intriguing phenomena from unconventional superconductivity to topological orders. Here, we report the coexistence of two interacting charge-density-wave (CDW) orders in EuTe_{4}, a layered crystal that has drawn considerable attention owing to its anomalous thermal hysteresis and a semiconducting CDW state despite the absence of perfect Fermi surface nesting. By accessing unoccupied conduction bands with time- and angle-resolved photoemission measurements, we find that monolayers and bilayers of Te in the unit cell host different CDWs that are associated with distinct energy gaps. The two gaps display dichotomous evolutions following photoexcitation, where the larger bilayer CDW gap exhibits less renormalization and faster recovery. Surprisingly, the CDW in the Te monolayer displays an additional momentum-dependent gap renormalization that cannot be captured by density-functional theory calculations. This phenomenon is attributed to interlayer interactions between the two CDW orders, which account for the semiconducting nature of the equilibrium state. Our findings not only offer microscopic insights into the correlated ground state of EuTe_{4} but also provide a general nonequilibrium approach to understand coexisting, layer-dependent orders in a complex system.

Anomalous thermal hysteresis and the diffuseness of phase transitions in K1–x (NH4) x H2PO4 solid solutions

The diffuseness of ferroelectric (FE) and antiferroelectric (AFE) phase transitions (PTs) in FE–AFE solid solutions of the K1–x(NH4)xH2PO4 type is discussed. A distinct correlation between the PT diffuseness parameter and the width of a PT temperature hysteresis is found. It is shown that these parameters of FE compositions are largely determined by the electrostatic interaction of random-field defects with interphase and domain boundaries.

Anomalous thermal hysteresis of two first order phase transitions in relaxor ferroelectric 0.945 Pb(Zn1/3Nb2/3)O3-0.055PbTiO3 crystals studied by Brillouin scattering

The thermal hysteresis has been studied by Brillouin scattering in the relaxor ferroelectric (1 − x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 with x = 0.055 (i.e., below the morphotropic phase boundary composition x ∼ 0.08). On heating from room temperature, the first order rhombohedral to tetragonal phase transition occurs at TR-T = 397 K, then the first order tetragonal to cubic transition occurs at TT-C = 425 K. However, on cooling from high temperature, only the diffusive phase transition was observed around TC-R = 401 K. Such anomalous thermal hysteresis is attributed to the metastable non-equilibrium states induced by supercooling due to quenching of nano-domains by the random electric fields of the B-site charge disorder.

Spectral assignments in the infrared absorption region and anomalous thermal hysteresis in the interband electronic transition of vanadium dioxide films.

The metal-insulator transition (MIT) is of key importance for understanding the fundamental electronic interaction that determines the physical properties of vanadium dioxide (VO2) film. Here, the spectral slopes of transmittance and reflectance in the infrared absorption region (about 0.62-1.63 eV) and the interband electronic transitions for VO2 films with thicknesses of 27, 40 and 63 nm have been investigated. The potential applications of the spectral slopes were presented in detail. It is found that the variation of resistivity and transmittance increases with the spectral slopes of transmittance and reflectance. It is surprising that the resistivity of the VO2 film with a thickness of 27 nm is larger than that of the VO2 film with a thickness of 40 nm in the metal state. In addition, an anomalous counterclockwise thermal hysteresis with higher energy from the interband electronic transition was also found during the MIT process for the thinnest film. It is believed that this remarkable phenomenon could be related to the correlation effects in the rutile phase, which could lead to the splitting of the a1g band into Hubbard bands. The lower Hubbard band would result in an electronic transition blue-shift with the empty e band, which can explain the origin of the counterclockwise thermal hysteresis and the abnormal resistivity in the metal state.

Cluster-glass behavior correlated with spin reorientation in Yb1−x Pr x FeO3

The magnetic properties of polycrystalline Yb1−xPrxFeO3 (0≤x≤0.9) are systematically investigated. A cusp in the zero-field-cooled dc magnetization and a frequency-dependent peak in the ac susceptibility reveal the glassy behaviors in this system. Interestingly, for YbFeO3, the freezing temperature Tf is just in the narrow spin-reorientation region of single-crystal YbFeO3 reported previously. The frequency-dependent peak in the real part of the ac susceptibility can be described by critical slowing down of spin dynamics. The fit to this critical slowing down law yields the values τ0=2.79×10−7 s and zv=2.61. The value of τ0 is in good agreement with values found in cluster-glass systems. Anomalous thermal hysteresis in the field-cooled magnetization is found in all samples, with a crossover point between the field-cooled cooling and field-cooled warming curves. These anomalous thermal hysteresis behaviors are explained by the competing interaction between the iron-ion subsystem and rare-earth-ion subsystem.

Electron Spin Resonance Study of <I>α</I>-Cr<SUB>2</SUB>O<SUB>3</SUB> and Cr<SUB>2</SUB>O<SUB>3</SUB>·<I>n</I>H<SUB>2</SUB>O Quasi-Spherical Nanoparticles

The quasi-spherical nanoparticles of hydrated Cr2O3 · nH2O, and crystalline α-Cr2O3, have been synthesized by reduction of the first row (3d) transition metal complex of K2Cr2O7. The temperaturedependence of electron spin resonance (ESR) spectrum was studied in terms of g-factor, line width and intensity. ESR of both Cr2O3 · nH2O and α-Cr2O3 has been studied at X-band (9.61 GHz) in the temperature range of 292–420K. An anomalous thermal hysteresis was observed in the ESR intensity and linewidth (∆Hpp of Cr2O3 · nH2O. This study shows that there could be a dominant water loss/gain during the heating-cooling cycles which is influencing the thermal relaxation time of Cr2O3 · nH2O. A similar hysteresis was observed in the differential scanning calorimetry (DSC) data which correlates well with that of ESR indicating possible surface dehydration/rehydration of Cr2O3 ·nH2O nanoparticles during the heating–cooling cycles of ESR measurements.

Anomalous thermal hysteresis in dielectric permittivity of CaCu3Ti4O12

We herein report an anomalous thermal hysteresis in dielectric permittivity in CaCu3Ti4O12. The anomalous behavior was well explained in terms of the low-temperature Maxwell–Wagner relaxation induced by frozen carriers. A multirelaxation mechanism, i.e., the coupling of the dipole relaxation to the frozen carrier-induced and blocked carrier-induced Maxwell–Wagner relaxations in the low-temperature and high-temperature regions, respectively, is proposed to be the origin of the colossal dielectric constant.

Anomalous thermal hysteresis in the SmC* phase of 10FHBBBM7*, revealed by dielectric measurements

The SmC* phase of (R)-4-(1-methylheptyloxycarbonyl)phenyl 4'-(4-decyloxy-3-fluorobenzoyloxy)-benzoate, 10FHBBBM7*, shows an anomalous thermal hysteresis that is reflected in the values of the measured dielectric constant. When the cooling-heating cycle is repeated, a memory effect occurs. In this work, we present a detailed study and a tentative interpretation of this unusual effect.

Relaxation effects in perovskite ferroelectric ceramics with smeared phase transition

In solid solutions with a perovskite structure PbZrO3-K0.5Bi0.5TiO3 and PbZrO3 — PbTiO3 the behaviours of low-frequency internal friction, dielectric permittivity and dielectric losses have been investigated at a change of temperature, bias electric field, as well as at isothermal annealing of samples. In structures, close to morphotropic phase transition, anomalous thermal hysteresis of dielectric losses, which is characterised by a long-term relaxation of metastable states is found out.

Incommensurable and glassy behaviour of Cd2-Nb2-O7 oxide pyrochlore single crystals

Abstract Low-frequency studies of the complex dielectric permittivity of Cd2Nb2O7 single crystals in the temperature range of 4–80 K are reported. Above Tcom ≃ 46 K an anomalous thermal hysteresis of ∊′ over the frequency range of 10 kHz-2 MHz as well as dielectric relaxation may be related to the existence of discommensurations and their dynamics. In the vicinity of Tf ≃ 18 K the temperature and frequency behavior of ∊∗ is typical of orientational glasses. Two relaxation process fitted with the Vogel-Fulcher law and the Arrhenius law take place near Tf. The first process is related to frustration in displacements of the “;seventh”; oxygens relative to Cd2+ ions and is characterized by freezing in of Cd-0(7) orientations below T0 ≃ 7 K. The Arrhenius-type process is related to relaxation of ferroelastic and ferroelectric domain walls.

Anomalous thermal hysteresis at the lock-in transitions in BCCD

Abstract Measurements of the dielectric constant and pyroelectric coefficient in BCCD reveal anomalous thermal hysteresis and memory effects. These effects are understood as being due to the pinning of the incommensurate modulation in the vicinity of the lock-in transitions.

Thermal hysteresis of the dielectric constant and anomalous behaviour of the raman soft mode damping of Cd2Nb2O7

Between 46 K > T > 80 K the dielectric constant of Cd2Nb2O7 shows an anomalous thermal hysteresis which is a characteristic feature of the incommensurate phase. In the Raman spectrum below Ttr = 80 K there appears a soft mode. Decline of its damping slows down between 46 K > T > 80 K, whereas its integrated intensity drops discontinuously at Ttr = 46 K. This soft mode of Cd2Nb2O7 behaves like the soft mode in the incommensurate phase of K2SeO4 and Rb2ZnBr4, and such behaviour of the soft mode damping and integrated intensity is not observed at usual structural phase transitions. These experimental facts suggest the existence of the incommensurate phase in Cd2Nb2O7 between Tc = 46 K and Ti = 80 K. Anomalous behaviour of the soft mode is believed to be due to the contributions of the first-order Raman scattering from the amplitudon (q = 0) and the second-order Raman scattering involving the amplitudon (q = 0) and the phason (q = Ki). When the amplitudon damping is taken as TA ∼ (Ti — T)-1, the relative cont...

Metal-semiconductor Transition with Anomalous Thermal Hysteresis Observed in Hexagonal (Ni1−xFex)1−yS, (0≤x≤0.30, 0≤y≤0.035)

Abstract The phase relation of (Ni1−xFex)1−yS system was determined by the X-ray powder diffraction method. Fe1−yS can be dissolved in Ni1−yS in ca. 30 at.%. Transition temperature (Tt) was measured mainly by the DSC method. Tt increases with increase in Fe contents. Tt in the forward direction, however, shows a significant increase as high as 50 degrees, when specimens are aged at a temperature below Tt. The reverse transformation is not affected by thermal hystory at all. This is explained by the relaxation process in which the strain energy stored in the low temperature phase is relieved by aging.