Electro-optical properties of Cu:KTa0.57Nb0.43O3 crystal near the FE-PE phase transition region

Heat capacities and thermodynamic properties of Cu xZn 1− xSiF 6·6H 2O ( x=1, 0.06, and 0) from 14 to 300 K

The present work reports a detailed study of the spin dynamics, magnetocaloric effect and critical behaviour near the magnetic phase transition temperature, of a ferrimagnetic spinel Cu1.5Mn1.5O4. The dynamic magnetic properties investigated using frequency-dependent ac magnetic susceptibility fitted using different phenomenological models such as Neel–Arrhenius, Vogel–Fulcher and power law, strongly indicate the presence of a cluster-glass-like behavior of Cu1.5Mn1.5O4 at 40 K. The magnetization data have revealed that our compound displays an occurrence of second-order paramagnetic (PM) to ferrimagnetic (FIM) phase transition at the Curie temperature TC = 80 K as the temperature decrease. In addition, the magnetic entropy change (ΔSM) was calculated using two different methods: Maxwell relations and Landau theory. An acceptable agreement was found between both sets of data, which proves the importance of both electron interaction and magnetoelastic coupling in the magnetocaloric effect (MCE) properties of Cu1.5Mn1.5O4. The relative cooling power (RCP) reaches 180.13 (J kg−1) for an applied field at 5 T, making our compound an effective candidate for magnetic refrigeration applications. The critical exponents β, γ and δ as well as transition temperature TC were extracted from various techniques indicating that the magnetic interaction in our sample follows the 3D-Ising model. The validity of the critical exponents is confirmed by applying the Windom scaling hypothesis.

Cu-poor and Cu-rich metallic precursors were prepared by cosputtering from In and Cu–Ga alloy targets and then partially selenized using H2Se gas. The properties of Cu(In,Ga)Se2 (CIGS) films are comparatively studied and the phase transition process is analyzed. The cosputtered metallic precursor has a rough morphology mostly covered by large In-rich nodules. After selenization, a large number of crumblike InSe grains were formed from the nodules on the surface of the Cu-rich film, whereas the Cu-poor film shows a dense surface. The selenized films comprise CIGS, Cu9(In,Ga)4 intermetallic, and the InSe phases. The proportion of the Cu9(In,Ga)4 phase in the Cu-rich film is more than that in the Cu-poor film. After annealing, the residual Cu9(In,Ga)4 of the Cu-poor film is eliminated. A negligible effect of Cu/(In+Ga) on the grain size can be observed. The CIGS solar cell with an efficiency of 15.1% was prepared by this method.

We studied the phase change and resistive switching characteristics of copper oxide (Cu x O) films through post-thermal annealing. This investigation aimed to assess the material’s potential for a variety of electrical devices, exploring its versatility in electronic applications. The Cu x O films deposited by RF magnetron sputtering were annealed at 300, 500, and 700 °C in ambient air for 4 min by rapid thermal annealing (RTA) method, and then it was confirmed that the structural phase change from Cu2O to CuO occurred with increasing annealing temperature. Resistive random-access memory (ReRAM) devices with Au/Cu x O/p+-Si structures were fabricated, and the ReRAM properties appeared in CuO-based devices, while Cu2O ReRAM devices did not exhibit resistive switching behavior. The CuO ReRAM device annealed at 500 °C showed the best properties, with a on/off ratio of 8 × 102, good switching endurance of ∼100 cycles, data retention for 104 s, and stable uniformity in the cumulative probability distribution. This characteristic change could be explained by the difference in the grain size and density of defects between the Cu2O and CuO films. These results demonstrate that superior and stable resistive switching properties of RF-sputtered Cu x O films can be obtained by low-temperature RTA.

Theoretical studies of optical properties of Cu doped rocksalt CdS

Tunable dielectric, electro-optic, and photoluminescence properties of Cu- and Gd-doped ZnO nanocomposites in E7 liquid crystals for device applications

Morphology, optical and electrical properties of Cu–Ni nanoparticles in a-C:H prepared by co-deposition of RF-sputtering and RF-PECVD

Coupling of a phase transition to electron and phonon transports provides extra degree of freedom to improve the thermoelectric performance, while the pertinent experimental and theoretical studies are still rare. Particularly, the impaction of chemical compositions and phase transition characters on the abnormal thermoelectric properties across phase transitions are largely unclear. Herein, by varying the Cu content x from 1.75 to 2.10, we systemically investigate the crystal structural evolution, phase transition features, and especially the thermoelectric properties during the phase transition for Cu x Se. It is found that the addition of over-stoichiometry Cu in Cu x Se could alter the phase transition characters and suppress the formation of Cu vacancies. The critical scatterings of phonons and electrons during phase transitions strongly enhance the Seebeck coefficient and diminish the thermal conductivity, leading to an ultrahigh dimensionless thermoelectric figure of merit of ∼1.38 at 397 K in Cu2.10Se. With the decreasing Cu content, the critical electron and phonon scattering behaviors are mitigated, and the corresponding thermoelectric performances are reduced. This work offers inspirations for understanding and tuning the thermoelectric transport properties during phase transitions.

In‐situ X‐ray and neutron diffraction investigations on Cu3N indicate the onset of a high‐pressure phase transition at about 5 GPa. The tetragonal cell parameters of the high‐pressure phase reveal a discontinuous volume decrease of about 20 %. The phase transition is reversible, with a hysteresis of about 2 GPa. Subsequent ex‐situ investigations in a multi‐anvil press evidence a reversible re‐formation of ambient pressure Cu3N from XRD patterns. The structure refinement with nitrogen atoms disordered in distorted octahedral voids of a tetragonal body‐centered copper substructure leads to an occupation of approximately 1/3 and thus to a composition of Cu3N1.0(1). Optical absorption measurements (IR‐VIS) up to 10 GPa indicate a semiconductor–metal transition. Density‐functional based total energy calculations concerning the proposed high‐pressure phase of Cu3N strongly support the experimental findings of a pressure‐induced phase transition above 6 GPa to a structure with a copper tetragonal body‐centered sublattice and nitrogen atoms in distorted octahedral voids. However, the calculations identify a need for an ordered alternative to provide the tetragonal distortion within the range of the observed c/a ratio. The resulting lattice parameters and the transition pressure fit with the measured data. For the case of an ordered occupation of the copper bct octahedral voids, all observed properties are in good agreement with the calculations.

Polycrystalline Cu(In,Ga)Se/sub 2/ (CIGS) thin films, grown by coevaporation of the constituent elements with different amounts of sodium (Na), were investigated. In some devices, an increased Na content was achieved through the incorporation of a thin layer of NaF deposited on the substrate prior to the growth of CIGS. The effect of Na on the electro-optical properties was addressed through characterization of the finished devices using photoluminescence (PL) and capacitance techniques. Results indicate the beneficial effect of Na as evidenced by increases in the device efficiency, open-circuit voltage, and PL intensity. Furthermore, these measurements provide evidence that Na (1) increases the net carrier concentration, and (2) reduces the number of gap states including those that act as minority-carrier traps.

The phase transitions and associated magnetic properties of Ni2Mn0.55Cu0.35Fe0.10Ga have been studied by dc magnetization and electrical resistivity measurements. A tetragonal crystal structure was identified at room temperature by powder x-ray diffraction measurements. The temperature dependence of magnetization data obtained while heating revealed two distinct transitions at 338 K and 368 K. On cooling the transitions were observed at 334 K and 355 K. The lower temperature transition showed a thermal hysteresis of ≈4 K, while the higher temperature transition exhibited a thermal hysteresis of ≈13 K. The temperature dependence of the electrical resistivity and isothermal entropy changes obtained data indicated that the transition at 338 K is a second order transition while the one at 368 K is a first order phase transition. For a field change of 5 T, a maximum entropy change of −3.5 J kg−1 K−1 has been observed. The experimental data showed that for both heating and cooling the martensitic phase transition occurred in a paramagnetic state in Ni2Mn0.55Cu0.35Fe0.10Ga.

The structural properties, phase transitions, and electronic structures of Cu2ZnSnS4 (CZTS) in the three structures have been researched using the first-principles density functional theory (DFT). The results indicate that the energies of stannite (ST) and pre-mixed Cu–Au (PMCA) CZTS are higher than those of kesterite (KS) CZTS, indicating that the KS CZTS is more stable. We found the phase transition pressure between the KS and ST structures of CZTS is about 32 GPa. Moreover, for KS- and PMCA-CZTS, there exists in the mischcrystal phase between 52 GPa and 65 GPa. The band structures show that the KS- and ST-CZTS are direct band gap semiconductors. The band gaps of three-type CZTS increase with increasing pressure, and the maximum band gap of KS and ST structures for CZTS occurs at 50 GPa. However, PMCA CZTS possesses metal property. Furthermore, the PMCA CZTS translates from metal to the indirect semiconductor with increasing pressure. The results play an important role in future experimental and theoretical work for CZTS materials.

A study of high-pressure single-crystal X-ray diffraction and luminescence experiments together with ab initio simulations based on the density functional theory has been performed for two isomorphous copper(I) halide compounds with the empirical formula [C8H6Cu2X2N2] (X = Br, I) up to 4.62(4) and 7.00(4) GPa for X-ray diffraction and 6.3(4) and 11.6(4) GPa for luminescence, respectively. An exhaustive study of compressibility has been completed by means of determination of the isothermal equations of state and structural changes with pressure at room temperature, giving bulk moduli of K0 = 14.4(5) GPa and K′0 = 7.7(6) for the bromide compound and K0 = 13.0(2) GPa and K′0 = 7.4(2) for the iodide compound. Both cases exhibited a phase transition of second order around 3.3 GPa that was also detected in luminescence experiments under the same high-pressure conditions, wherein redshifts of the emission bands with increasing pressure were observed due to shortening of the Cu–Cu distances. Additionally, ab initio studies were carried out which confirmed the results obtained experimentally, although unfortunately, the phase transition was not predicted.

The experimental data about crystal structures, phase transitions and dielectric properties of Cu(II) and Mn(III)-containing complex perovskites are analysed. The principal result is that the presence of Jahn-Teller cations in oxygen octahedra of perovskites is favourable for the origination of spontaneously polarized state (SPS).

Following the discovery of a charge-density wave in the cubic chalcogenide spinel Cu${\mathrm{V}}_{2}$${\mathrm{S}}_{4}$, the other known copper chalcogenide spinels were synthesized and their magnetic susceptibility measured to look for similar phase transitions. No phase transitions were observed in these other compounds. The present data also show that the electrons in metallic Cu${\mathrm{V}}_{2}$${\mathrm{S}}_{4}$ are highly correlated (the magnetic susceptibility is greatly enhanced). Data concerning the effects of alloying and nonstoichiometry on the magnetic properties of Cu${\mathrm{V}}_{2}$${\mathrm{S}}_{4}$ are also presented.