Clear Thermal Hysteresis Research Articles

Investigation on structural, dielectric, and impedance characteristics of Zr-modified NaNbO3 ceramics at elevated temperature

NaNb 1 − x Zr x O 3 (NZr) ceramics with 0 ≤ x ≤ 0.15 are prepared via solid-state reaction route. Structural, microstructural, and electronic state investigations of NZr samples were performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS), respectively. Rietveld refinement reveals that NZr samples crystallize in the orthorhombic phase similar to room temperature P b m a phase of NaNbO 3 . Minor quantities of ZrO 2 are detected for higher NZr-composition, which suppress the grain growth of NZr ceramics. XPS reveals that small amount of Zr substitution in NaNbO 3 also creates an ambiance of unbalanced charge neutrality. The dielectric characteristics of NZr samples are investigated from -190 to 450 °C temperature range in frequency window 1 KHz–1 MHz for both the heating and cooling cycles. A clear thermal hysteresis loop is obtained in each composition and the observed anomaly corresponds to P (AFE) - R (AFE) polymorphic phase transition. As x grows, ϵ ′ (T) becomes more dispersive and strongly depend on applied field. The activation energy obtained from the analysis of Arrhenius relation indicates that the oxygen vacancies are responsible for conduction process of the material. Impedance analysis confirms the NTCR behavior and non-Debye relaxation of the material. • The polycrystalline NZr ceramics are prepared by solid state reaction method. • Small amount of Zr dopant creates an ambiance of unbalanced charge neutrality. • The AFE (P) to AFE (R) phase transition is confirmed by ɛ ’ (T) analysis. • Impedance spectroscopic studies reveal the NTCR behavior of NZr ceramics. • The non-Debye type nature of material is verified by Nyquist analysis.

Hall voltage reversal and structural phase transition in VO2 thin films

In this work, we investigated the nanoscale conduction and charge transport characteristics of epitaxial VO2 thin films around the metal-insulator transition (MIT) using the Hall transport measurement and conduction atomic force microscopy. Unlike the conventional oxides, the VO2 thin films show unique transport characteristics. First, the dominant carrier type shows a critical change from electron to hole during the MIT sequence (cooling sequence) or from hole to electron during the reverse MIT sequence (heating sequence). Second, the carrier density measured during the MIT sequence is higher than that measured during the reverse MIT sequence, evidenced with a clear thermal hysteresis. Third, the volume fraction (area percentage) of the nanoscale high-conduction phase also shows a thermal hysteresis, evidenced with a larger volume fraction of the high-conduction region in the MIT sequence than the reverse MIT sequence. The first-principles calculations indicate that the dominant carrier is the hole in the monoclinic phase, while it is the electron in the rutile phase, suggesting that the unique charge transport characteristics are attributed to the structural phase transition. Our work provides a deep insight into the nanoscale conduction and charge transports in VO2 thin films.

Detection of anomalies in NLO sulphamic acid single crystals by ultrasonic and thermal studies

The ultrasonic pulse echo overlap technique (PEO) has been used to measure the velocities of 10 MHz acoustic waves in sulphamic acid single crystals in the range of 300–400 K. This study evaluated all the elastic stiffness constants, compliance constants and Poisson’s ratios of the crystal. The temperature variations of the elastic constants have been determined. The phase transition studies above room temperature were investigated using ultrasonic PEO technique. This study has suggested new weak elastic anomalies for the crystal around 330 K. The transverse elastic constants C 44 and C 66 have shown clear thermal hysteresis of 2 K. The present differential scanning calorimetric (DSC) studies carried out at a slow heating rate have also suggested weak phase transition around 331 K. The present elastic and thermal studies have been substantiated by already reported DC electrical conductivity studies around 330 K.

Multiple magnetic transitions and associated room temperature magneto-functionality in Ni2.048Mn1.312In0.64

Present work reports on the observation of multiple magnetic transitions in a Ni-excess ferromagnetic shape memory alloy with nominal composition Ni2.048Mn1.312In0.64. The magnetization data reveal two distinct thermal hystereses associated with two different phase transitions at different temperature regions. The high temperature magnetic hysteresis is due to the martensitic phase transition whereas the low temperature hysteresis occurs around the magnetic anomaly signifying the transition from a paramagnetic-like state to the ferromagnetic ground state within the martensite. Clear thermal hysteresis along with the sign of the curvatures of Arrott plot curves confirm the first-order nature of both the transitions. In addition, the studied alloy is found to be functionally rich with the observation of large magnetoresistance (−45% and −4% at 80 kOe) and magnetocaloric effect (+16.7 Jkg−1K−1 and −2.25 Jkg−1K−1 at 50kOe) around these two hysteresis regions (300K and 195K respectively).

First-order magnetic and magnetostructural transitions in the magnetocaloric compound MnNi0.73Fe0.27Ge

Magnetic and magnetostructural transitions of MnNi0.73Fe0.27Ge have been studied by calorimetry and by magnetic measurements. The first-order MST from paramagnetic to ferromagnetic martensite shows a giant magnetic entropy change of −27J/kgK for a magnetic-field change of 50kOe around 233K. A weak first-order magnetic transition is observed in the martensite phase over a large low-temperature range, with clear thermal hysteresis and increased saturation field. The origin is discussed on the basis of the competitiom between ferromagnetic and antiferromagnetic coupling with magneto-elastic coupling.

Investigation of magnetic and electrical transport properties of Dy2Ni2Sn

The magnetic and transport properties of the ternary rare-earth compound Dy2Ni2Sn are reported. The compound undergoes a long range antiferromagnetic ordering below TN=43K with a collinear structure. A second transition is observed below about Tt=28K, where spin canting takes place. We find clear thermal hysteresis in our magnetization data between 20 and 45K, indicating the first order nature of the magnetic transitions occurring at TN and Tt. Clear signature of metamagnetism is observed in the canted antiferromagnetic phase. The change in entropy on the application of magnetic field (magnetocaloric effect) was calculated from the isothermal magnetization data and it shows negative and positive peaks at TN and Tt respectively. The thermal variation of resistivity shows clear peak like signature near TN, which gets suppressed under applied magnetic field resulting negative magnetoresistance. The low temperature resistivity (below Tt) can be well fitted with the model available for spin dependent s–f scattering in antiferromagnetic system having well localized moments. The data also indicate short range correlations well above the antiferromagnetic transition point, which might be related to the two dimensional spin–spin correlations in this layered compound.

Charge Density Wave and Superconducting Properties in Single Crystals of Lu5Ir4Si10

We measured the electrical resistivity from 2K up to 900K on high quality single crystals of Lu5Ir4Si10. A clear thermal hysteresis was found at the onset of the Charge Density Wave (CDW), evidencing the first order nature of the transition. When tantalum is included in the compound, the CDW is destroyed and the superconducting critical temperature is enhanced. Finally, we present specific heat and magnetic penetration depth in the Meissner state. We show that the superconducting properties are very close to a weak coupling BCS superconductor.

Temperature-induced exciton switching in long alkyl chain based inorganic-organic hybrids

Photoluminescence and transmission is systematically explored in thin films of long–alkyl-chain-based inorganic-organic (IO) hybrids (CnH2n+1NH3)2PbI4 (n = 12, 16, 18) (CnPI) and NH3C12H22NH3PbI4 (DDPI). Such IO-hybrids, which form natural multiple quantum well structures stacked up along c-axis, possess strong room-temperature exciton transitions. These hybrids exhibit reversible phase transition of two different crystal phase transitions at easily accessible device temperatures. Flipping the structural phase is clearly reflected in switching of the excitons with corresponding photoluminescence and transmission changes showing clear thermal hysteresis. The phase-dependent switching of excitons is predominantly due to reversible crumpling of the inorganic PbI sheet networks. Systematic temperature dependent studies establish a correlation between the structure and optical exciton features. Such thermo-optic exciton switching suggests possible new photonic devices.

Room-temperature Magnetocaloric Effect in (Co 0.35Mn 0.65) 2P Compound

The (Co 0.35 Mn 0.65 ) 2 P compound, prepared by a mechanical alloying plus solid sintering process, exhibits a second-order transition from a ferromagnetic state to a paramagnetic one at Curie temperature of about 320 K with no clear thermal hysteresis. A magnetic-entropy change (Δ S M ) value above 1.6 J·kg −1 ·K −1 for a 5 T field change is obtained in the whole temperature range of 292.5–352.5 K and the maximum value of the Δ S M is 2.3 J·kg −1 ·K −1 at 337.5 K. The study on the magnetocaloric effect of the (Co 0.35 Mn 0.65 ) 2 P compound may be helpful for exploring good candidates for room-temperature magnetic refrigeration.

Critical Behavior at the SmC*α−SmC* Phase Transition Studied by High Sensitivity DSC

Calorimetric measurements have been done to investigate the smectic-C*α(SmC*α)- smectic-C*(SmC*) transition using high sensitivity differential scanning calorimetry. It was found that the SmC*α−SmC* transition for a liquid crystalline compound 11OHFBBB1M7 shows a first-order transition with a clear thermal hysteresis while other two compounds, LN36 and 12OTBBB1M7, exhibit continuous behaviors which support the existence of the critical point and also the slow relaxation dynamics encountered with the change in the helical pitch.

Phase Transition and Structural Analysis of (Li,Na,K)NbO<sub>3</sub> Lead-Free Piezoelectric Ceramics

Structural characterization of various (Li,Na,K)NbO3 solid solutions with different Li contents has been carried out by temperature-variable Raman scattering measurement. It was found that there was no clear thermal hysteresis between orthorhombic-tetragonal phase transition in the heating/cooling processes for (Li,Na,K)NbO3 ceramics with Li content of 6 wt% and above, although a noticeable thermal hysteresis is observed in the Raman spectra and dielectric constant measurement for the other specimens with lower Li contents. It is presumed that the structural change of (Li,Na,K)NbO3 cell tends to become insensibility against temperature as the Li content increases above 6.0 mol%.

NMR study of the gelation of a designed gelator

The gelation of a designed gelator was investigated by different NMR methods, which showed a clear thermal hysteresis. Two very simple approaches for the NMR determination of the gelation point are suggested. One involves the observation of the NMR integral, and the other records the ratio of the diffusion coefficients between the gelator and the solvent. Differential behavior of the gelator protons are interpreted as a hint that a part of the gelator molecule might still be flexible as in the dissolved state.

Transport and magnetic properties inYBaCo2O5.45: Focus on the high-temperature transition

The electronic transport properties and the magnetic susceptibility were measured in detail in $\mathrm{Y}\mathrm{Ba}{\mathrm{Co}}_{2}{\mathrm{O}}_{5.45}$. Close to the so-called metal-insulator transition, strong effects of resistance relaxation, a clear thermal hysteresis, and a sudden increase of the resistance noise are observed. This is likely due to the first order character of the transition and to the underlying phases coexistence. A positive and linear magnetoresistance is also observed, which can be linked to this heterogeneity. From a magnetic point of view, the paramagnetic to ordered magnetic state transition is observed using nonlinear susceptibility. This transition shows the characteristics of a continuous transition, and time dependent effects can be linked with the dynamics of magnetic domains in the presence of disorder. Thus, when focusing on the order of the transitions, the electronic one and the magnetic one cannot be directly associated.

Transport, magnetic and structural investigations of Co–Ni–Al shape memory alloy

The transport, magnetic and structural properties of the ferromagnetic shape memory alloy with nominal composition Co 1.28Ni 1.17Al have been investigated. The alloy shows long range ferromagnetic order below 269 K. The anomaly due to the martensitic transition is observed in the resistivity and magnetization data in the temperature range around 175 K, which is associated with clear thermal hysteresis. A significant magneto-thermal irreversibility between the zero-field-cooled and the field-cooled data is observed below the martensitic start temperature. The structural change is confirmed by temperature dependent X-ray diffraction, and our analysis indicate that both martensite and austenite phases mutually coexist in the region of hysteresis. Existence of distinct minor hysteresis loops in the resistivity data is also in accordance with a metastable region of phase coexistence across the martensitic transition.

Magnetic and martensitic transitions in Ni–Fe–Ga alloy

The ferromagnetic shape memory alloy with nominal composition Ni 54Fe 19Ga 27 is investigated by Ac susceptibility and resistivity measurements. The alloy shows long-range ferromagnetic order below 290 K. The anomaly due to the martensitic transition is observed in the susceptibility and resistivity data in the temperature range around 220 K, which is associated with clear thermal hysteresis. Minor hysteresis loop technique was used to investigate the phase coexistence across the martensitic transition, and our analysis indicate that both martensite and austenite phases mutually coexist in the region of hysteresis.

Study of first-order metal-insulator transition in the strongly correlated electron system Y 1 − xCa xTiO 3

The metal-to-insulator (MI) transition in the Y 1 − x Ca x TiO 3 system is known to occur at x = 0.35. Furthermore, near this critical metallic region, electrical resistivity and magnetic susceptibility show a broad peak around 170 K and are accompanied by clear thermal hysteresis. This thermal hysteresis in magnetic susceptibility is found to vanish at 1.05 GPa. These phenomena can be interpreted as some aspects of a first-order type metal-insulator transition.