[en] A series of the double-doping samples La_(2+4x)/3Sr_(1-4x)/3Mn_1-xCu_xO₃(0=< x=<0.2)with the Mn³⁺/Mn⁴⁺ ratio fixed at 2:1 and the single-doping samples La_2/3Sr_1/3Mn_1-xCu_xO₃(0=< x=<0.2) have been investigated. For the double-doping samples, though the ratio Mn³⁺/Mn⁴⁺=2:1 has been generally recognized the optimum ratio, the Curie temperature T_C and metallic-insulator transition temperature T_p1 are more rapidly decreased by Cu substitution than that corresponding to single-doping samples. And the resistivity ρ value for the double doping is larger about two or three orders of magnitude than that corresponding to single doping. At the same time, two resistivity peaks and two magnetoresistance (MR) peaks appear. We suggest that for the double-doping samples the A-site cation size < r_A> and the A-site mismatch factor σ² decreases with increasing doping level, which leads to the system microstructural distortion. This microstructural distortion makes the Mn³⁺-O-Mn⁴⁺ cut off more cluster-spin except for the clusters induced by Cu. These cluster interfaces contribute to ρ, which exceeds far the contribution of e_g electron decreasing with doping increasing in the single doping. At the same time, such interface scattering also gives rise to the appearance of second peak for the double-doping samples. The experimental results shows that double doping could be also a potential way in tuning colossal MR (CMR), which can give a guide for the adequate selection of CMR materials

[en] Highlights: • Explorations on salt hydrates with melting points ranging from 75 to 95 °C are required. • Performance evaluation on salt hydrates in applications is different from experiments. • Multiple heat transfer enhancements can improve the performance of latent heat storage. • Latent heat storage using salt hydrates in centralized building heating is promising. -- Abstract: In this forward-looking perspective, the current research status of latent heat storage using salt hydrates for building heating are firstly analyzed from aspects of material development, performance evaluation, heat transfer enhancement and application feasibility. Based on the analysis, barriers for the further promotion of this technology, including narrow application range, imperfect performance evaluation, inefficient heat transfer enhancement and vague market prospect are outlined. To address these issues, perspectives on four aspects are provided. First, further explorations on salt hydrates with high melting points meeting the heat dispatching demand of centralized building heating are strongly recommended. Second, effects of supercooling and phase separation of salt hydrates in practical applications should be considered differently from lab-scale experiments. Third, the combination of multiple heat transfer enhancement approaches can further improve the overall performance of heat storage. Fourth, this technology has a certain prospect in high-temperature heat dispatching in densely populated areas and short-distance mobile heat supply for emergency. The above perspectives provide guidelines for the future material development, device design, system optimization, and application scenario selection of latent heat storage using salt hydrates for building heating.

[en] The effects of La-doping on the structural, magnetic, electrical transport and specific-heat properties in 4d perovskites Sr_1-xLa_xMoO₃ (0≤x≤0.2) have been investigated. The substitution of Sr ions by La ions does not change the space group of the samples, but increases the lattice parameter a (Aa). The resistivity ρ and magnetic susceptibility χ decrease monotonously with the increase of x, while the electronic specific heat coefficient γ _e increases. The resistivity of all samples shows a T² dependence in the low-temperature region of 2 K< T<125 K and a T dependence in the high-temperature range of 130 K< T<350 K, related to the electron-electron (e-e) and electron-phonon (e-ph) scattering, respectively. The specific-heat data agrees with the classical Dulong-Petit phonon specific heat, C_cl=3k_BrN_A=124.7 J/mol K at high temperatures and C_p(T)/T=γ_e+ β_pT² at low temperatures. These behaviors can be explained according to the decrease of the density of states (DOS) at the Fermi energy level (E_F), N(E_F). (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] The sensitivity of transport and the lattice to a direct current has been investigated by means of in situ measurements of resistivity ρ and Young's modulus E along with magnetic measurements in La_0.67-yPr_yCa_0.33MnO₃ (y=0, 0.15, 0.25, and 0.30) compounds. Increasing the Pr doping level enhances the softening of the magnitude of E with the appearance of a minimum in the curve of the temperature dependence of the modulus, E(T). The direct current depresses the resistivity and shifts the E(T) minimum to lower temperatures dramatically for the compounds with y≥0.25, which exhibit a distinct magnetic hysteresis loop. The resistivity drop caused by the larger current may result from the depression of the Q₃-type distortion mode of Mn³⁺O₆ octahedra by the current, which may favor the lower resistivity. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] We present a systematic study of the structure, magnetization, resistivity, and Hall effect properties of pulsed laser deposited Fe- and Cu-codoped In₂O₃ and indium-tin-oxide (ITO) thin films. Both the films show a clear ferromagnetism and anomalous Hall effect at 300 K. The saturated magnetic moments are almost the same for the two samples, but their remanent moments M_r and coercive fields H_C are quite different. M_r and H_C values of ITO film are much smaller than that of In₂O₃. The ITO sample shows a typical semiconducting behavior in whole studied temperature range, while the In₂O₃ thin film is metallic in the temperature range between 147 and 285 K. Analysis of different conduction mechanisms suggest that charge carriers are not localized in the present films. The profile of the anomalous Hall effect vs. magnetic field was found to be identical to the magnetic hysteresis loops, indicating the possible intrinsic nature of ferromagnetism in the present samples.

[en] Polycrystalline sample of the new layered superconductor Bi₄O₄S₃ is successfully synthesized by solid-state reaction method by using Bi, S and Bi₂O₃ powders with one-step solid state reaction. The superconducting transition temperature (T_c^onset=4.5K), the zero resistance transition temperature (T_c0 = 4.07 K) and the diamagnetic transition temperature (4.02 K at H = 10 Oe) were confirmed by electrical transport and magnetic measurements. Also, our results indicate a typical type II-superconductor behavior and the charge carriers are mainly electron-type. In addition, a large thermoelectric effect was observed with a dimensionless thermoelectric figure of merit (ZT) of about 0.03 at 300 K.

[en] The effect of Co doping on the magnetic and transport properties of La_0.7Sr_0.3Mn_1-xCo_xO₃ (0≤x≤0.5) is investigated. The Co doping at Mn sites dilutes the double-exchange interaction between Mn³⁺ and Mn⁴⁺ ions and changes the long-range ferromagnetic (FM) order of La_0.7Sr_0.3MnO₃ (LSMO) to the spin glass (SG) or cluster glass (CG) state for samples with x ≥ 0.1. For x≥0.3, the paramagnetic (PM) metal to FM metal transition of LSMO disappears and the temperature dependence of resistivity ρ(T) follows semiconducting behavior in the whole measured temperature region with the resistivity increasing by orders of magnitude. An interesting result is that ρ(T) exhibits an obvious anomaly at T* ∝ 100 K, which is ascribed to the spin-state transition of Co ions. For samples with x=0.1 and 0.3, magnetoresistance (MR) effects are markedly enhanced in the low-temperature region compared with undoped LSMO, which is suggested to originate from the appearance of spin-dependent tunneling magnetoresistance. However, for samples with x=0.5, the MR effect is suppressed over the entire temperature region measured and an obvious exchange anisotropy phenomenon, characterized by the shift of the hysteresis loop, is also observed, which is ascribed to the marked increase of the antiferromagnetic insulating phase. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] We report the effects of Cu doping on the physical properties of the newly discovered layered superconductor Bi_4−xCu_xO₄S₃ (0≤x≤0.15). The superconductivity is suppressed gradually with increasing x and finally disappears when x>0.10. Meanwhile the temperature dependent resistivity changes it slope from positive x<0.1 to negative x≥0.1. The lattice constant c decreases initially with x, but increases with increasing x further. However, the lattice constant a (=b) always reduces with x. The suppression of superconductivity and the change of the ρ(T) slope may be attributable to a shift of the Fermi energy level due to Cu doping

[en] Graphical abstract: - Highlights: • Multiple temperature-induced magnetization reversals were observed in x = 0.1. • Coexistence of normal and inverse magnetocaloric effects was observed. • A reasonable model was proposed to explain the magnetization reversals. - Abstract: The structural and magnetic properties of the SmCr_1−xFe_xO₃ (0 ≤ x ≤ 0.5) system have been investigated. Multiple temperature-induced magnetization reversals were observed in x = 0.1. The high-temperature magnetization reversal is due to the special spin structure, in which the net canted moment of the Cr-rich regions and the net moment of the Fe–Cr ordered regions orient in opposite direction; while the low temperature one can be ascribed to the spin reorientation. The sample with x = 0.5 exhibits the highest compensation temperature. Coexistence of normal and inverse magnetocaloric effects was observed in all doped samples. Potential applications in magnetic refrigeration based constant temperature bath near room temperature (∼286 K) have been demonstrated

[en] The effects of Mn substitutions on the crystal structure, magnetic properties, and magnetocaloric effect (MCE) of antiperovskite Sn_1−xCMn_3+x (0≤x≤0.40) have been investigated detailedly. Both the Curie temperature (T_C) and the magnetizations at 40 kOe decrease with increasing x firstly for x≤0.10, and then increase with increasing x further. The type of magnetic transition changes from first-order to second-order around x=0.10 with increasing x. Chemical composition-dependent MCE is also studied around T_C. With increasing x, the maximal magnetic entropy changes decrease and the magnetic phase transitions broaden. Accordingly, the relative cooling power (RCP) increases with increasing x, reaching the largest values of ∼0.56 J/cm³ (∼75 J/kg) and ∼1.66 J/cm³ (∼221 J/kg) with the magnetic changes of 20 kOe and 48 kOe, respectively. Considering the large RCP, inexpensive, and innoxious raw materials, these serial samples Sn_1−xCMn_3+x are suggested to be potential room-temperature magnetic refrigerant materials. - Highlights: ► Around x=0.10, the type of FM–PM transition changes from first- to second-order. ► Curie temperature reduces firstly and then increase with increasing x. ► Magnetocaloric effect shows strong chemical composition-dependence. ► For x=0.30 and 0.40, the value of T_C can exceed 300 K. ► Largest RCP can reach ∼0.56 J/cm³ and ∼1.66 J/cm³ under 20 and 48 kOe, respectively.