Mössbauer study of hydrided amorhous Fe−M−Zr (M=Co,Cr) alloys

Mössbauer spectra of hydrided amorphous Fe₉₀?_xCo_xZr₁₀ (A_x) and Fe₉₀?_yCr_yZr₁₀ (B_y) (x=4, 10, 20; y=0, 4, 7, 13, 16, 20) are studied. For low hydriding time values (t), the average hyperfine field \(\left( {\bar B_{hf} } \right)\) and isomer shift δ_is show a drastic increase which can mainly be associated with the volume effect. For higher (t) values, an electron transfer effect can be responsible for the hyperfine parameter variation. The influence of hydrogenation on magnetic anisotropy is also discussed.     

Superionic conductivity of the heterovalent solid solutions R 1−x M x F 3−x (R=REE, M=Ca, Ba) with tysonite-type structure

The fluorine-ion conductivity of anion-deficient solid solutions R _1−x Ca_xF_3−x and R _1−x Ba_xF_3−x having the tysonite (LaF₃) structure was investigated by the impedance spectroscopy method. R _1−x Ca_xF_3−x (R=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho) and R _1−x Ba_xF_3−x (R=La, Pr, Nd) single crystals were grown from the melt by the Bridgman-Stockbarger method. The electrophysical measurements were performed in the frequency range 5−5×10⁵ and temperature range 300–700 K. The temperature dependences of the electrical conductivity for the crystals studied is determined by the migration of fluorine anions along various structural positions. It is shown that, from the standpoint of increasing the conductivity of tysonite matrices RF₃ (R=La, Pr, Nd), doping by CaF₂ and BaF₂ is less promising than SrF₂. Fiz. Tverd. Tela (St. Petersburg) 41, 638–640 (April 1999)     

Ionic and electronic transport in perovskite-type La(Ga,M)O3−δ (M=Mg, Cr, Fe, Co, Ni, Nb)

Oxygen ion conduction in La_0.9Sr_0.1Ga_1−xM_xO_3−δ (M=Cr, Fe; x=0 – 0.20), LaGa_1−xM_xO_3−δ (M=Co, Ni; x=0.20 – 0.60), LaGa_1−x−yCo_xMg_yO_3−δ (x=0.35 – 0.60; y=0.10 – 0.25) and LaGa_0.85−xMg_0.15(Nb_0.33Mg_0.66)_xO_3−δ (x=0 – 0.20) is reported. At temperatures below 1200 K the ionic conductivity of La(Ga,M)O_3−δ (M=Co, Ni) increases with increasing oxygen nonstoichiometry, but is lower than for La(Ga,Mg)O_3−δ and (La,Sr)GaO_3−δ. Co-doping with Nb and Mg was found to result in decreasing ionic transport in La(Ga,Nb,Mg)O_3−δ due to blocking of oxygen sites by Nb⁵⁺. Small additions of Fe to the B-site of La_0.9Sr_0.1GaO_3−δ increase the ionic conductivity, whereas substitution of Cr for Ga has the opposite effect. Incorporation of transition metal cations into the Ga site leads to a higher p-type electronic conductivity in all studied perovskites. Paper presented at the 6th Euroconference on Solid Sate Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

A comparative study of cationic distribution in the systems Li1+5XM1−XO3 and Li1+XM1−XM′ XO3 (M=Nb,M′=Ti; M=Ta,M′=Ti,Zr, Sn)

Abstract

A comparative ferroelectric and NMR studies of the systems Li_1+5X M_1?XO₃ and Li_1+XM_1?XM^′ _XO₃ (M=Nb, M′=Ti M = Ta; M′=Ti, Zr, Sn) have indicated that plot of T_C versus composition can be qualitatively explained on the basis of cationic distribution. The strong drop of T_C has been found in systems with all cations in octahedral sites, whereas little change of T_C was observed along the solid solutions with Li-ions in interstitial tetrahedral sites.     

Frequency response of the low-temperature ionic conductivity of single crystals R 1 − y M y F3 − y (R = La-Er; M = Ca, Sr, Ba, Cd)

The frequency response (10^?1–10^?7 Hz) of the ionic conductivity σ of R _{1 ? y} M _y F_{3 ? y} single crystals (R is a rare-earth element, and M stands for an alkaline-earth element and Cd) with a tysonite structure is studied over a wide temperature range (114–410 K), which includes (for the first time for these phases) the interval below room temperature. The dependences σ(ν) obtained are discussed within the hopping relaxation model. The characteristics of the relaxation and migration processes and the carrier concentration and mobility are determined.     

Electronic structure and magnetic properties of RCo5−xMx (R=Y,Pr and M=Al,Si) system

Detailed theoretical and experimental investigations of the electronic and magnetic properties of the RCo_5?xM_x compounds (R=Y, Pr and M=Si, Al) have been performed. All theoretical investigations of the electronic and magnetic properties of the system have been done using the Korringa–Kohn–Rostoker (KKR) band structure method. The Si for Co substitution in RCo₅ does not change the magnetic ordering: the RCo_5?xSi_x with R=Y, Nd and Pr is ferromagnetic, whilst the heavy rare-earth containing compounds are ferrimagnetic. The important modifications induced by this substitution concerns the magnetic properties of the system: the Curie temperature and the magnetic moments of Co decrease with Si content, indicating the weakening of the Co–Co exchange interaction. The band structure calculations evidence the hybridization between the 3d electronic states of Co and the 3p states of Si as possible reason for the diminishing of Co–Co exchange interaction. Also, the volume effect on the magnetic properties of the YCo₄Si was investigated using theoretical methods. The results are compared with the experimental measurements in order to distinguish the origin of magnetization reduction in YCo₄Si compared with YCo₄Al.     

Structure and properties of the anions MF4−, MCl4− and MBr4− (M = C,Si, Ge)

Density functional theory (DFT), Møller–Plesset (MP2) and coupled cluster with single and double substitutions including non-iterative triple excitations (CCSD(T)) calculations on the anions MX₄^?, with M = C, Si, Ge and X = F, Cl, Br, show that GeF₄^?, SiCl₄^?, GeCl₄^? and SiBr₄^? prefer a C_2v conformation, but CCl₄^? is an elongated C_3v structure. CBr₄^? has T_d symmetry in MP2, but is slightly more stable in elongated C_3v form with DFT and CCSD(T). GeBr₄^? has T_d symmetry. CF₄^? and SiF₄^? are unstable with respect to loss of an electron. Vertical electron affinities (EAs) are negative also for CCl₄ and SiCl₄, and close to zero for GeF₄ and SiBr₄. Adiabatic EAs range from 0.47 eV for SiCl₄ to 1.78 eV for GeBr₄. The lowest excited states at T_d symmetry are ²T₂ resonances with energies of 2.1–3.5 eV, resulting from excitation of the a₁ singly occupied molecular orbital to vacant t₂ orbitals. Vertical excitation energies (VEEs) and vibrational frequencies are given for the most stable anionic geometries. Comparison with experimental VEEs for CCl₄^? is made. From dissociation energies of MX₄, MX₄^?, MX₃ and MX₃^?, appearance energies of X^?, MX₃^?, X₂^? and MX₂^? were calculated. Most were found to be in reasonable agreement with experimental values. Theoretical spin densities and g-factors have been compared with experimental results available for CCl₄^?, SiCl₄^? and GeCl₄^?.     

Quantum-chemical modeling of the electronic structure and magnetic properties of Sn1 − x − y M x Sb y O2, M = Cr, Mn, Co, or Ni (x = 0.25; y = 0, 0.25)

The electronic and magnetic structures of the Sn_0.75 M _0.25O₂ and Sn_0.5 M _0.25Sb_0.25O₂ (M = Cr, Mn, Co, Ni) compounds with a structure that is derivative of the rutile structure are modeled using the ab initio spin-polarized tight-binding linear muffin-tin orbital (TB-LMTO) method. The magnetic moments of the transition metal atoms are calculated. The data obtained are used to analyze the influence of the composition of Sn_{1 ? x ? y} M _x Sb _y O₂ phases on their electronic spectra and the magnetic and transport characteristics.     

Y(Fe,M)12化合物的电子结构与磁性(M=Nb,Si)

采用新近发展的全势能线性缀加平面波((L)APW) 局域轨道(lo)和广义梯度近似(GGA)密度泛函方法计算了Y(Fe,M)12化合物(M=Nb,Si)的电子结构,得到了相应的总态密度和局域态密度,并分析了替代原子与替代晶位不同引起态密度的变化。根据计算结果预测的居里温度变化与实验结果基本一致。     

Tunneling and point-contact spectroscopy of high-T c superconductors M−Ba2Cu3O7 (M=Y,La, Eu)

Tunneling and point-contact measurements have been performed on different high-T _c superconductors M–Ba₂Cu₃O₇ with M=Y, La, Eu. The average energy gaps deduced from the tunneling spectra are about 2=33 meV for the Y- and La-type samples and about 2=38 meV for the Eu-type samples, which give ratios 2/k _B T _c in the range from 4 to 6. The point-contact characteristics show a distinct minimum in the differential resistance about zero bias and additional sharp spikes up to 40 mV. From these pointcontacts we can give an estimate of the critical current, yielding values in the range from 0.2 to 3 mA.     

Crystal structure and magnetic properties of pseudoternary TbRh2−xMxSi2(M = Ru,Ir) compounds

The structural and magnetic characteristics of the pseudoternary TbRh_2−xM_xSi₂(M = Ru, Ir) compounds were studied. The compounds crystallize in the tetragonal ThCr₂Si₂-type structure. The magnetic data were collected in the temperature range 70–300 K. Their magnetic susceptibilities satisfy the Curie-Weiss law in the temperatures higher than 130 K. The magnetic moment of the rare earth atom is larger than of the free Tb³⁺ ion. A modified RKKY theory with included interaction between the conduction electrons was applied to explain the variation of properties of the compounds.     

Magnetic and crystallographic properties of substituted Pr2Fe14−xMxB compounds (M = Si,Ga, CrandCu)

Structural and magnetic properties of Pr₂Fe_14−xM_xB systems (M = Si, Ga, CrandCu) are investigated. These compounds crystallize in a tetragonal system of P4₂/mnm-type for a Si content up to x = 2, Cr content up to x = 3 and for Ga and Cu concentration up to x = 1. The Curie temperature increases when Fe is substituted by Si, Ga and Cu, decreases when Fe is replaced by Cr. The saturation magnetization decreases with increasing content of an M element. The rate of the decrease is larger than that expected by a simple dilution model. The influence of M atoms on the anisotropy field is discussed.     

Electronic spectroscopy of some isoelectronic MM′(CO)10 (M,M′ = Mn,Cr, Tc,Mo, Re,W) from time-dependent density functional theory

The electronic spectra of 12 isoelectronic binuclear decacarbonyls MM′(CO)₁₀ have been calculated, using time-dependent density functional theory (TD-DFT). The geometry has been optimised using the B3LYP functional. The energy of some well-known bands is calculated with the same functional for Mn₂(CO)₁₀ and other compounds as a test, using the same functional. The calculated values for the energy and the oscillator strength are in good fitting with experimental and reference data, and they show very small dependence on the basis. Then, the same calculation has been carried out for all the compounds up to 150 states. The strongest calculated transitions are summarised and assigned.     

Mössbauer effect studies of Sm(Rh1−xFex)3B2, x=0.005

Sm(Rh_1–xFe_x)₃B₂ compound (x=0.005) was studied by⁵⁷Fe Mossbauer spectroscopy as a function of temperature. The Fe doped compound has high temperature magnetic transition T_c ^*580 K in addition to the transition at T_c90 K exhibited by the pure SmRh₃B₂ compound. For Tc ^* the spectrum comprises of a quadrupole doublet along with magnetic splitting which merges into a single quadrupole doublet above T_c ^*. The results indicate that Fe induces a large polarization in the Rh-4d band due to the enhanced density of states at the Fermi level in the presence of the hybridized Sm 4f-electrons.     

Evaluation of the electrical capacitance of M,O2/O2− interfaces (M=Pt, Au, Pd, In2O3; O2− = zirconia based electrolyte) exhibiting constant phase element behavior

The behavior of the electrode systems M,O₂/O² (M = porous Pd, Pt, A and dense In₂O₃; O²⁻ = ZrO₂-based single-crystal solid electrolyte) was studied by means of impedance measurements. The examination of the Pt,O₂/O²⁻ electrode system showed that the constant phase element (CPE) can be attributed to a nonuniform distribution of current at the electrode surface. It was observed that the CPE parameters n and B in the expression Y_CPE = B (jω)ⁿ may be related by B=(C_dl)ⁿ (R_Ω)_n-1, where C_dl is the double layer capacitance and R_Ω the resistance of the electrolyte in the cell. Then, C_dl of the electrode - electrolyte interface could be determined. The specific C_dl of the oxidized noble metals and india electrodes is nearly one order of magnitude lower than C_dl of the electrodes in the metallic state. The C_dl value of all the electrodes studied depends little or is independent of temperature and oxygen pressure. It is concluded that the Helmholtz model of double layer structure does not contradict the C_dl behavior.     

A study of the system Ag3−xTlxFe(CN)6, (x =0, 1, 2, 3) by Mössbauer spectroscopy

The ferricyanides Ag_3−xTl_xFe(CN)₆, (x = 0, 1, 2, 3) have been measured by Mössbauer spectroscopy. The results indicate a negative EFG for all samples except for x = 1, that is positive. The isomer shift for Tl₃Fe(CN)₆ is the more negative, indicating a strong contribution from the empty p-orbitals of Tl⁺ ions.     

M2CeO4(M=Ca,Sr,Ba)的结构与发光特性

SSr2CeO4是一种新型的一维结构发光材料，其特殊的结构对其发光特性有决定性的作用。Sr2CeO4体系中可以顺利地进行能量传递，产生较强电荷迁移发光。合成了M2CeO4(M=Ca,Sr,Ba），发现与Sr2CeO4具有类似结构的Ba2CeO4也可以发光，而结构完全发生了变化的Ca2CeO4则不发光。