共查询到20条相似文献,搜索用时 15 毫秒
1.
R.R. Sun X.Y. Qin L.L. Li D. Li J. Zhang Y.S. Zhang C.J. Tang 《Journal of Physics and Chemistry of Solids》2014
The Ruddlesden–Popper (RP) phase compounds (Sr0.95R0.05)3Ti2O7 (R=Er, Y, Dy, Gd, Eu, Sm, Nd and La) were prepared, and their transport and thermoelectric properties were investigated. The results indicate that high-T electrical resistivity ρ (300 K<T<1000 K) increases monotonically with temperature and basically has a relation ρ∝TM, with M varying from 0.91 to 1.92 at temperatures T>~650 K, suggesting acoustic phonon scattering is dominant. At low temperatures (5 K<T<300 K), ρ for (Sr0.95R0.05)3Ti2O7 (R=Nd and La) decreases monotonously with decreasing temperature, whereas ρ for (Sr0.95R0.05)3Ti2O7 (R=Er, Y, Dy, Gd, Eu and Sm) decreases first, and then increases instead as T decreases to a critical temperature Tc. Moreover, electrical conductivity σ∝T1/2 holds at lower temperatures, indicating that the electron–electron interaction caused by the presence of disorder dominates the transport process at the low temperatures. Besides, experiments show that at T<~400 K the lattice thermal conductivity of the doped compounds basically decreases with increase of the atomic mass of dopants. Generally, the figure of merit (ZT) at 1000 K increases first, and then decreases with the increase of the dopants' ionic radius, and the largest ZT is achieved in (Sr0.95Gd0.05)3Ti2O7 mainly owing to its lower lattice thermal conductivity. 相似文献
2.
Single phase perovskite Sr2CuNbO6−δ with a high proportion of Cu1+ ions and oxygen vacancies was synthesized by solid-state reaction. The structure was determined by Rietveld method with space group Pm3m. Isotropic g value was evaluated from electron spin resonance (ESR) measurements. The ESR result is consistent with that of magnetic susceptibility. 相似文献
3.
A.A. Lavrentyev I.Ya. Nikifororv A.L. Ankudinov 《Journal of Physics and Chemistry of Solids》2003,64(12):2479-2486
The electronic structure of phosphorus-contained sulfides InPS4, Tl3PS4, and Sn2P2S6 was investigated experimentally with X-ray spectroscopy and theoretically by quantum mechanical calculations. The partial densities of electron states calculated with the ab initio multiple scattering FEFF8 code correspond well to their experimental analogues—the X-ray K- and L2,3-spectra of sulfur and phosphorus. The good agreement between theory and experiment was also achieved for K-absorption spectra of S and P in the investigated sulfides. In spite of the difference in the crystallographic structure of InPS4, TI3PS4, and Sn2P2S6 that influence the form of K-absorption spectra, the electronic structure of their valence bands are rather similar. This is due to the strong interaction of the P and S atoms, which are the nearest neighbors in the compounds studied. The electron densities of p- and s-states of phosphorus are shifted by about 3 eV to lower energies in comparison to the analogous electron states of sulfur. This is connected with the greater electro-negativity of sulfur, and is confirmed by the calculated electron charge transfer from P to S. 相似文献
4.
J. Raittila T. Salminen K. Schlesier 《Journal of Physics and Chemistry of Solids》2006,67(8):1712-1718
Double perovskite Sr2FeMoO6 powders with small crystallite size have been synthesised with citrate-gel method. The starting solution pH was varied between 1.5 and 9.0 resulting in large differences in the phase composition and ordering of B′/B″ sites. The samples prepared at 975 °C had crystallite sizes under 40 nm whereas crystallite sizes of the samples prepared at 1050 °C were between 78 and 239 nm. The XRD patterns were refined with spacegroup I 4/m, which gave good results for both batches, although clearly better results were obtained with monoclinic P 21/n spacegroup for the 975 °C batch. The ordering and the saturation magnetization agreed well with each other after treatment at 1050 °C, but the samples prepared at 975 °C had a strongly reduced saturation magnetization from that given by the ordering. 相似文献
5.
C.A. Triana L.T. CorredorD.A. Landínez Téllez J. Roa-Rojas 《Physica B: Condensed Matter》2012,407(16):3150-3154
The crystal structure evolution of the Sr2GdRuO6 complex perovskite at high-temperature has been investigated over a wide temperature range between 298 K≤T≤1273 K. Powder X-ray diffraction measurements at room temperature and Rietveld analysis show that this compounds crystallizes in a monoclinic perovskite-type structure with P21/n (#14) space group and the 1:1 ordered arrangement of Ru5+ and Gd3+ cations over the six-coordinate M sites, with lattice parameters a=5.81032(8) Å, b=5.82341(4) Å, c=8.21939(7) Å, V=278.11(6) Å3 and angle β=90.311(2)o. The high-temperature analysis shows that this material suffers two-phase transitions. At 373 K it adopts a monoclinic perovskite structure with I2/m space group, and lattice parameters a=5.81383(2) Å, b=5.82526(4) Å, c=8.22486(1) Å, V=278.56(2) Å3 and angle β=90.28(2)o. Above of 773 K, it suffers a phase transition from monoclinic I2/m to tetragonal I4/m, with lattice parameters a=5.84779(1) Å, c=8.27261(1) Å, V=282.89(5) Å3 and angle β=90.02(9)o. The high-temperature phase transition from monoclinic I2/m to tetragonal I4/m is characterized by strongly anisotropic displacements of the anions. 相似文献
6.
This paper presents a study of bulk samples synthesized of the Ag1−xCuxInSe2 semiconductor system. Structural, thermal and electrical properties, as a function of the nominal composition (Cu content) x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 were studied. The influence of x on parameters such as melting temperature, solid phase transition temperature, lattice parameters, bond lengths, crystallite size t (coherent domain), electrical resistivity, electrical mobility and majority carrier concentration was analyzed. The electrical parameters are analyzed at room temperature. In general, it is observed that the properties of the Ag1−xCuxInSe2 system for x≤0.4 are dominated by n-AgInSe2, while for x>0.4, these are in the domain of p-CuInSe2. The crystallite size t in the whole composition range (x) is of the order of the nanoparticles. Secondary phases (CuSe, Ag2Se and InSe) in small proportion were identified by XRD and DTA. 相似文献
7.
Takahiro Iijima Keigo Hamada Kazunaka Endo 《Journal of Physics and Chemistry of Solids》2005,66(6):1101-1106
The temperature dependences of 2H NMR spectra and spin-lattice relaxation time T1 have been measured for paramagnetic [Mn(H2O)6][SiF6]. The obtained 2H NMR spectra were simulated by considering the quadrupole interaction and paramagnetic shift. The variation of the spectra measured in phase III was explained by the 180° flip of water molecules. The activation energy Ea and the jumping rate at infinite temperature k0 for the 180° flip of H2O were obtained as 35 kJ mol−1 and 4×1014 s−1, respectively. The spectral change in phases I and II was ascribed to the reorientation of [Mn(H2O)6]2+ around the C3 axis where the Ea and k0 values were estimated as 45 kJ mol−1 and 1×1013 s−1, respectively. From the almost temperature independent and short T1 value, the correlation time for electron-spin flip-flops, τe, and the exchange coupling constant J were obtained as 3.0×10−10 s and 2.9×10−3 cm−1, respectively. The II-III phase transition can be caused by the onset of the jumping motion of [Mn(H2O)6]2+ around the C3 axis. 相似文献
8.
The transport properties of Sr0.98La0.02SnO3−δ in the system Sr1−xLaxSnO3−δ, after which the pyrochlore La2Sn2O7 appears, were investigated over the temperature range 4.2-300 K. The oxide was found to be n-type semiconductor with concomitant reduction of Sn4+ into Sn2+. The magnetic susceptibility was measured down to 4.2 K and is less than 3×10−5 emu cgs mol−1 consistent with itinerant electron behavior. The electron is believed to travel in a narrow band of Sn:5s character with an effective mass ∼4 mo. The highest band gap is 4.32 eV and the optical transition is directly allowed. A further indirect transition occurs at 4.04 eV. The electrical conductivity follows an Arrhenius-type law with a thermal activation of 40 meV and occurs by small polaron hopping between nominal states Sn4+/2+. The linear increase of thermo-power with temperature yields an electron mobility μ300 K (2×10−4 cm2 V−1 s−1) thermally activated. The insulating-metal transition seems to be of Anderson type resulting from random positions of lanthanum sites and oxygen vacancies. At low temperatures, the conduction mechanism changes to a variable range hopping with a linear plot Ln ρ−1 vs. T−4. The photo electrochemical (PEC) measurements confirm the n-type conductivity and give an onset potential of −0.46 VSCE in KOH (1 M). The Mott-Schottky plot C−2-V shows a linear behavior from which the flat band potential Vfb=+0.01 VSCE at pH 7 and the doping density ND=1.04×1021 cm−3 were determined. 相似文献
9.
Lina Sun Peng Wu Jingtao Liu Huang Zhou Shengyong Jin Jiangying Wang 《Journal of Physics and Chemistry of Solids》2011,72(10):1147-1151
Microstructure, phase transformation behavior and dielectric properties of BaTi1−x(Al1/2Nb1/2)xO3 (0.01≤x≤0.40) ceramics were investigated. A high level of (Al1/2Nb1/2)4+ substitution for Ti4+ ions was not conducive to the stability of the perovskite structure and resulted in the formation of BaAl2O4. As x was increased, lattice constants and unit cell volume decreased, reached a minimum at x=0.10 and then increased. The BaTi1−x(Al1/2Nb1/2)xO3 ceramics at room temperature experienced a transformation from ferroelectric to paraelectric phase with increasing (Al1/2Nb1/2)4+ concentration. Meanwhile, permittivity of the BaTi1−x(Al1/2Nb1/2)xO3 ceramics was markedly reduced, while Q value was slightly increased. Frequency dispersion of dielectric peak was obviously increased as x was increased from 0.01 to 0.10. It is of great interest that a dielectric abnormity represented by a broad dielectric peak at 200-400 K was observed for the composition with x=0.40. 相似文献
10.
G. Narsinga Rao Saibal Roy Chung-Yuan Mou J.W. Chen 《Journal of magnetism and magnetic materials》2006
We have investigated the magnetotransport and magnetic properties on polycrystalline samples of Sr2−xLaxFeMoO6 (x=0, 0.2, 0.4, 0.6, 0.8 and 1.0). The magnitude of intergrain tunneling magnetoresistance with low magnetic field of 0.88 T for x=0.2 and 0.4 samples are as large as 5% and 7% at room temperature and 13% and 10% at 10 K, respectively. The increase of coercivity (Hc), ratio of remanent magnetization with respect to saturation magnetization (Mr/Ms), high saturation fields, and reduction of the saturation magnetization indicate that random disorder of spin orientation is mainly responsible for enhancement of the low-field magnetoresistance for samples with x?0.4. Whereas rapid drop of Hc, Mr/Ms, Mr, and saturation fields for samples with x>0.4 signifies the growth of antiphase boundary, which gives rise to lower values of low-field MR. 相似文献
11.
A. Bhattacharjee P.J. van Koningsbruggen Joel S. Miller 《Journal of Physics and Chemistry of Solids》2008,69(11):2713-2718
The 57Fe Mössbauer spectroscopy of mononuclear [Fe(II)(isoxazole)6](ClO4)2 has been studied to reveal the thermal spin crossover of Fe(II) between low-spin (S=0) and high-spin (S=2) states. Temperature-dependent spin transition curves have been constructed with the least-square fitted data obtained from the Mössbauer spectra measured at various temperatures between 84 and 270 K during a cooling and heating cycle. This compound exhibits an unusual temperature-dependent spin transition behaviour with TC(↓)=223 and TC(↑)=213 K occurring in the reverse order in comparison to those observed in SQUID observation and many other spin transition compounds. The compound has three high-spin Fe(II) sites at the highest temperature of study of which two undergo spin transitions. The compound seems to undergo a structural phase transition around the spin transition temperature, which plays a significant role in the spin crossover behaviour as well as the magnetic properties of the compound at temperatures below TC. The present study reveals an increase in high-spin fraction upon heating in the temperature range below TC, and an explanation is provided. 相似文献
12.
Superconductivity and non-metallicity induced by doping the topological insulators Bi2Se3 and Bi2Te3
Y.S. Hor J.G. Checkelsky D. Qu R.J. Cava 《Journal of Physics and Chemistry of Solids》2011,72(5):572-576
We show that by Ca doping the Bi2Se3 topological insulator, the Fermi level can be fine tuned to fall inside the band gap and therefore suppresses the bulk conductivity. Non-metallic Bi2Se3 crystals are obtained. On the other hand, the Bi2Se3 topological insulator can also be induced to become a bulk superconductor, with Tc∼3.8 K, by copper intercalation in the van der Waals gaps between the Bi2Se3 layers. Likewise, an as-grown crystal of metallic Bi2Te3 can be turned into a non-metallic crystal by slight variation in the Te content. The Bi2Te3 topological insulator shows small amounts of superconductivity with Tc∼5.5 K when reacted with Pd to form materials of the type PdzBi2Te3. 相似文献
13.
A.M.R Teixeira O PillaF Rossi P.T.C Freire F.E.A MeloJ Mendes Filho V Lemos 《Journal of Physics and Chemistry of Solids》2002,63(10):1951-1956
Brillouin spectroscopy was used to study the phase transitions of LiK0.80(NH4)0.20SO4 mixed crystals in the temperature range 10-300 K. The relevant elastic stiffness coefficients were evaluated at room temperature. The quasi-longitudinal γ16 and the quasi-transverse γ17 mode frequencies were measured in the above temperature range. From their frequency vs. temperature curve, three different phase transitions were determined. Two of the four phases presented by the crystal were found to be ferroelastic. The observed phases are tentatively assigned through a comparison with the phase transitions undergone by LiKSO4 and LiK0.96(NH4)0.04SO4 crystals. An anomalous behavior of the Brillouin linewidth near the 260 K phase transition was observed. 相似文献
14.
A. Martínez-de la Cruz F.E. Longoria Rodríguez 《Journal of Physics and Chemistry of Solids》2008,69(4):830-834
Electrochemical lithium insertion into (PO2)4(WO3)2m, where m=9 and 10, has allowed the determination of several phases Lix(PO2)4(WO3)2m between 3.4 and 0.01 V vs Li+/Li0. After the first cycle the electrochemical system was unable to maintain the high specific capacity of the cells (540 Ah/kg) due to irreversible processes. Nevertheless at high voltage values, above 1.4 V vs Li+/Li0, the lithium insertion proceeded through a reversible mechanism. By means of X-ray diffraction experiments we have detected the nature of different phases Lix(PO2)4(WO3)2m formed and we have established a correlation with the reversible/irreversible processes detected during the electrochemical insertion. 相似文献
15.
Petra Á. Szilágyi Stéphane Dorbes José Antonio Real Christophe Faulmann 《Journal of Physics and Chemistry of Solids》2008,69(11):2681-2686
Thermal and pressure effects have been investigated on the [Fe(sal2-trien)][Ni(dmit)2] spin crossover complex by means of Mössbauer spectroscopic, calorimetric, X-ray diffraction and magnetic susceptibility measurements. The complex displays a complete thermal spin transition between the and spin states of FeIII near 245 K with a hysteresis loop of ca. 30 K. This transition is characterised by a change of the enthalpy, ΔHHL=7 kJ/mol, entropy, ΔSHL=29 J/Kmol, and the unit cell volume, ΔVHL=15.4 Å3. Under hydrostatic pressures up to 5.7 kbar the thermal transition shifts to higher temperatures by ca. 16 K/kbar. Interestingly, at a low applied pressure of 500 bar the hysteresis loop becomes wider (ca. 61 K) and the transition is blocked at ∼50% upon cooling, indicating a possible (irreversible) structural phase transition under pressure. 相似文献
16.
T. Kaji H. Ohta Y. Inagaki M. Azuma 《Journal of Physics and Chemistry of Solids》2005,66(11):2068-2071
Submillimeter and millimeter wave ESR measurements of spin gap systems SrCu2(PO4)2 and PbCu2(PO4)2, which have four kinds of dimers, have been performed to investigate the magnetic properties of spin gap systems using the pulsed magnetic field up to 35T. The observed ESR spectra of powder sample SrCu2(PO4)2 show sharp and single peak in the temperature range from 4.2 to 80 K. The anisotropy of the g-values turned out to be very small compared to the usual anisotropic powder spectra of copper compounds. The dynamical properties will be discussed from the temperature dependence measurements. 相似文献
17.
R. Checchetto N. Bazzanella P. Mengucci 《Journal of Physics and Chemistry of Solids》2008,69(9):2160-2163
We have prepared two different kinds of composite materials for hydrogen storage and studied their H2 storage capacity and desorption kinetics. The first composite material consists of magnesium-containing transition metal nanoclusters distributed in the Mg matrix (Mg:TM): this composite material shows better H2 desorption performances than pure Mg. This improvement is attributed to the role of the MgH2-TM nanocluster interface as preferential site for hexagonal Mg (h-Mg) nucleation and to the rapid formation of interconnected h-Mg domains where H diffusion during desorption occurs. The second composite material consists of LaNi5 particles (size<30 μm) distributed in a polymeric matrix. The H2 storage capacity is negligible at low metal content (50 wt%) when the metal particles are completely embedded in the polymeric matrix. The H2 storage capacity is comparable to that of the pure LaNi5 powders at high metal content (80 wt%) when a percolative distribution is assumed by the LaNi5 particles: this evidence points out the role of metal-metal interfaces and of interconnected metallic networks for H transport. 相似文献
18.
B Bednarska-BolekZ Ciunik R Jakubas G BatorP Ciapa?a 《Journal of Physics and Chemistry of Solids》2002,63(3):507-518
New triethylammonium salts: [(C2H5)3NH]SbCl6 (TCA) and [(C2H5)3NH]SbCl6·1/2[(C2H5)3NH]Cl (TCAT) have been synthesized. The compounds crystallise in monoclinic symmetry: space groups P21/n and P21/c, for TCA at 293 K and TCAT at 100 K, respectively. The crystal structure of [(C2H5)3NH]SbCl6 consists of discrete ionic pairs—triethylammonium cations and hexachloroantimonate anions—linked via the bifurcated N-H?Cl hydrogen bonds. The crystal structure of [(C2H5)3NH]SbCl6·1/2[(C2H5)3NH]Cl is composed of three symmetrically independent triethylammonium cations, chlorine anion and two symmetrically independent hexachloroantimonate anions. TCA undergoes a structural phase transition at 336 K (on heating) into the orthorhombic C222 space group, whereas TCAT reveals a structural phase transition at 332 K. The phase transitions are of the first order type. TCA shows a ferroelastic domain structure below 336 K. Differential scanning calorimetry, dilatometric, dielectric dispersion and Raman scattering measurements have been used to study the phase transition mechanisms in these triethylammonium salts. 相似文献
19.
S. Rani Anshu A. Agarwal N. Kishore V.P. Seth 《Journal of Physics and Chemistry of Solids》2008,69(7):1855-1860
Studies of structural and electrical properties have been carried out on a number of glasses with wide ranging compositions in the glass systems Li2O·MO·Bi2O3·B2O3 (where M=Zn or Cd), in order to understand the effect of transition metal (TM) ions on the structure of these glasses. The density and molar volume measurements have also been made to understand the structural changes occurring in these glasses. The dc conductivity measured in the temperature range 423-623 K obeys Arrhenius law. It increases with increase in Li2O/MO ratio. The results of infrared spectra indicate that TM ions (Zn2+ or Cd2+) behave as network former in the present system. Boron exists in both tri- and tetra-hedral units in these glasses and no boroxol ring formation takes place in the glass structure. Values of theoretical optical basicity have also been reported. 相似文献
20.
Bismuth selenotelluride (Bi2(Te0.9Se0.1)3) films were electrodeposited at constant current density from acidic aqueous solutions with Arabic gum in order to produce thin films for miniaturized thermoelectric devices. X-ray fluorescence spectroscopy determined film compositions. X-ray diffraction pattern shows that the films as deposited are polycrystalline, isostructural to Bi2Te3 and covered by crystallites. Mueller-matrix analysis reveals that the electroplated layers are optically like an isotropic medium. Their pseudo-dielectric functions were determined using mid-infrared spectroscopic ellipsometry. Tauc-Lorentz combined with Drude dispersion relations were successfully used. The energy band gap Eg was found to be about 0.15 eV. Moreover, the fundamental absorption edge was described by an indirect optical band-to-band transition. From Seebeck coefficient measurement, films exhibit n-type charge carrier and the value of thermoelectric power is about −40 μV/K. 相似文献