Structures of CsMgBr3, CsCdBr3 and CsMgI3— diamagnetic linear chain lattices

The diamagnetic salts, CsMgBr₃, CsCdBr₃ and CsMgI₃, are shown by X-ray diffraction studies to adopt the CsNiCl₃ structure. This hexagonal lattice possesses a distinct one-dimensional character. The divalent metal ions in these salts are surrounded by octahedral arrays of halide ions ; however, there is a noticeable trigonal distortion. The structures are compared with those of other one-dimensional AMX₃ salts.     

Electronic properties of Bi2O3 and MoO3 and relationships to oxidation catalysis

A semiempirical atom superposition and electron delocalization molecular orbital analysis of the bonding and electronic structure of MoO₃, oxygen deficient MoO₃, and the α, β, and δ phases of Bi₂O₃ has been made. It is found that both small — e.g. MoO₆ — and large — e.g. Mo₆O₂₄ — clusters are useful models for cation electronic structure within the theory used. From the calculations, an interpretation is given for all available optical and photoemission data for the oxides. The color, conductivity, and new photoemission peak of oxygen-deficient MoO₃ conducting bronzes are found to be due to the addition of electrons to the lowest of three Mo 5d bands which are empty in MoO₃. Weakly allowed d ← d transitions in the red are responsible for the color. Strongly allowed Mo 5d ← O 2p charge transfer excitations are responsible for the optical absorption above 3.2 eV. For the bismuth oxides, three occupied bands are found showing strong Bi 6s, 6p, 6d and O 2p hybridization. These bands have been seen experimentally. The highest band surprisingly has Bi 6p lone-pair character which is explained in terms of the relative Bi 6s and 6p and O 2p ionization potentials using perturbation theory. Rather similar electronic structures are found for the three phases despite their varying cation coordinations and structures. A charge transfer optical absorption edge at ～ 2.6 eV for the β form agrees well with observations reported in the literature, and similar edges should occur for the other phases. The cubic δ form has an unusual low-lying band suggesting absorption in the infrared. Our results provide insight into the surface properties of these oxides.     

Ground state properties of CsCoCl3

The electronic spectra of CsCoCl₃ are fit to a Hamiltonian that includes terms for interelectron repulsion, octahedral and trigonal crystal fields, and spin-orbit coupling. The fit adequately accounts for both the optical spectrum and the electronic Raman spectrum. The fitted parameters give empirical estimates of the radial expectation values 〈r^?1〉 and 〈r^?3〉 as well as the charge on the cobalt. The ground state wave functions generated from the fit are used to calculate the following properties: parallel and perpendicular g factors, Co hyperfine field, ⁵⁹Co quadrupole splitting, anisotropy of magnetic exchange, the magnetic moment of Co²⁺, and the spin flop field. The agreement between calculated values and observed values for this variety of independently obtained properties is reasonable in all cases.     

Electro- and thermoreflectance of Bi2Te3 and Bi2Se3

Electroreflectance measurements in Bi₂Te₃ and Bi₂Se₃ with the electric field vector of the incident light both inclined and perpendicular to the C-axis have been made at room temperature. The structures found by other workers in the reflection measurements are observed in the present experiment, together with new structures at 0.91 eV, 1.18 eV, 1.78 eV, and 2.61 eV in Bi₂Se₃ which are not related to formerly observed transitions. From these measurements, the selection rules for direct optical transitions in Bi₂Te₃ and Bi₂Se₃ are studied. Thermoreflectance measurements are also made at both room and liquid-nitrogen temperatures. The positions of the peaks obtained in the present work are compared with the electroreflectance and reflection data.     

Accurate determination of the interchain exchange in CsCoCl3 · 2H2O from detailed low-temperature susceptibility data

Detailed measurements of the b and c axis susceptibilities of CsCoCl₃ · 2H₂O have been made between 1.5 and 30 K. The results support the canted antiferromagnetic linear chain model previously used to describe this determine the value of the intrachain exchange. The results give J/k = ?52 ± 2 K and g_b = 4.18 ± 0.08. This value for J/k is significantly larger than what other investigators have reported for CsCoCl₃ · 2H₂O and if the Ising model is applicable it will be more accurate because of the simplicity of the analysis.     

Low temperature magnetostriction studies in CsNiCl3

The forced magnetostriction of the linear-chain antiferromagnet CsNiCl₃ has been measured from 1.6 to 20K. For the applied field parallel to the c-axis the data below the Néel temperature T_N clearly show the effects of the spin-flop near 20 kG. Effects ascribed to domain realignment are observed below 5 kG for the field normal to the c-axis. In the paramagnetic phase above T_N the magnetostrictive behavior conforms to a simple model in which the intrachain exchange J is a function only of the c-parameter. The resulting partial Grüneisen parameter $\text{γ∥}{}^{\mathrm{m}}\text{=}\text{?d(?nJ)}\text{d(?nc)}$ is compared with that obtained from thermal expansion measurements.     

High-field magnetic phase diagram of CsCoCl3 revised

A fine structure of high-field magnetization curves of CsCoCl₃ and related compounds is discussed. It is shown that a precursor of a high-field phase transition originates from nucleation of an intermediate high-field ferrimagnetic (IFM) phase. Since the IFM state is degenerate its growth starting from few nucleation centers gives rise to domain walls formation. Their creep also makes a contribution to the magnetization dynamics similar to slow relaxation in Ca₃Co₂O₆. An experimental verification of the model is proposed.     

掺入Mg2+对CsNiCl3晶体的基态能级、零场分裂参量及Jahn-Teller效应的影响

应用不可约张量理论构造了三角对称晶场中3d²/3d^８态离子的45阶可完全对角化的微扰哈密顿矩阵，在考虑了以前工作中被忽略的自旋-自旋耦合作用的基础上计算了CsNiCl₃晶体和CsNiCl₃:Mg²⁺晶体的基态能级、晶体结构、零场分裂参量和Jahn-Teller效应，研究了掺入Mg²⁺对CsNiCl₃晶体的光谱、零场分裂参量及Jahn-Teller效应的影响和自旋单重态对基态能级的贡献，发现掺杂使得晶体结构产生畸变，从而改变晶体光谱的精细结构和零场分裂参量，不改变Jahn-Teller效应的分裂规律但改变分裂的大小. 关键词： 基态能级 掺杂 零场分裂 自旋-自旋耦合     

Birefringence,X-ray and neutron diffraction measurements on the structural phase transitions of (CH3NH3)2 MnCl4 and (CH3NH3)2FeCl4

We used optical birefringence, X-ray and neutron diffraction methods with single crystals to study the structural phase transitions of the perowskite-type layer structures of (CH₃NH₃)₂MeCl₄ with Me=Mn, Fe. The Mn-compound shows the following structural transitions at 394 K — a continuous order-disorder phase transition from tetragonal symmetry $\text{I4}\text{mmm}$ to orthorhombic space group Abma (Cmca in reference 10); at 257 K — a discontinuous transition to a second tetragonal modification; at 95 K — a discontinuous transition to a monoclinic phase. For the Fe-compound the corresponding transition temperatures are 328 K and 231 K, respectively. A low temperature monoclinic phase could not be observed. The lattice parameters of the different modifications were determined as a function of temperature. The temperature dependent course of the order parameter has been investigated for the order—disorder transition. For both compounds, all the methods used gave the same value for the critical exponent of β = 0.315.     

Structural,electronic and optical properties of Ca3Bi2: First-principles investigation

In this work by applying first principles calculations structural, electronic and optical properties of Ca₃Bi₂ compound in hexagonal and cubic phases are studied within the framework of the density functional theory using the full potential linearized augmented plane wave (FP-LAPW) approach. According to our study band gap for Ca₃Bi₂ in hexagonal phase are 0.47, 0.96 and 1?eV within the PBE-GGA, EV-GGA and mBJ-GGA, respectively. The corresponding values for cubic phase are 1.24, 2.08 and 2.14?eV, respectively. The effects of hydrostatic pressure on the behavior of the electronic properties such as band gap, valence bandwidths and anti-symmetry gap are investigated. It is found that the hydrostatic pressure increases the band widths of all bands below the Fermi energy while it decreases the band gap and the anti-symmetry gap. In our calculations, the dielectric tensor is derived within the random phase approximation (RPA). The first absorption peak in imaginary part of dielectric function for both phases is located in the energy range 2.0–2.5?eV which are beneficial to practical applications in optoelectronic devices in the visible spectral range. For instance, hexagonal phase of Ca₃Bi₂ with a band gap around 1?eV can be applied for photovoltaic application and cubic phase with a band gap of 2?eV can be used for water splitting application. Moreover, we found the optical spectra of hexagonal phase are anisotropic along E||x and E||z.     

Nanoscale ab-initio calculations of optical and electronic properties of LaCrO3 in cubic and rhombohedral phases

We report nanoscale ab-initio calculations of the linear optical and electronic properties of LaCrO₃ in nonmagnetic cubic and rhombohedral phases using the full potential linear augmented plane wave (FP-LAPW) method. In this work the generalized gradient approximation is used for exchange-correlation potential. The dielectric tensor is derived within random-phase approximation. We present results for the band structure, density of states, imaginary and real parts of dielectric tensor, electron energy loss spectroscopy, sum rules, reflectivity, refractive index and extinction coefficient. The regions of transparent, absorption and reflection are discussed. We are not aware of any published experimental or theoretical data for these phases, so our calculations can be used to cover this lack of data for these phases.     

β-C3N4,β-Si3N4和β-Ge3N4的能带结构

采用基于密度泛函理论的线性丸盒轨道原子球近似(LMTO-ASA)从头计算方法,研究了β-C₃N₄,β-Si₃N₄和β-Ge₃N₄的能带结构,得到了它们的能隙分别为:4.1751,5.1788和4.0279eV。对于β-C₃N₄,由于N的部分2p电子占据了非键轨道,禁带宽度较窄;对于β-Si₃N_{4关键词：}     

Magnetic susceptibilities of polycrystalline samples of the compounds ANiCl3 (A = RB,NH4, Tl,Cs) and ANiBr3 (A = Rb,Cs)

The susceptibilities of polycrystalline samples of various antiferromagnetic linear-chain compounds ANiX₃ (A =Tl, NH₄, Rb, Cs and X = Cl, Br) have been measured in the temperature region 2–200 °K. The results, amongst which the already known data for RbNiCl₃ and CsNiCl₃, are interpreted in terms of a theory, developed by Weng, for antiferromagnetic Heisenberg linear-chain systems with spin S = 1. By means of Oguchi's Green function theory and the experimentally determined transition temperatures T_N the order of magnitude of the ratio between inter- and intra-chain interaction is obtained.     

Nuclear spin lattice relaxation in the linear antiferromagnet CsNiCl3

Anisotropic effects have been found in the low temperature (< 10 K) nuclear spin lattice relaxation rates in the linear paramagnet CsNiCl₃ in a strong magnetic field (～ 60 kOe). The existence of a small single ion anisotropy term may be the cause of these effects.     

The spin-flop transition in the nearly one-dimensional antiferromagnets RbNiCl3 and CsNiCl3

A spin-flop transition has been observed in the ordered phase of the nearly one-dimensional antiferromagnets RbNiCl₃ and CsNiCl₃$\text{H}{}_{\mathrm{s?:;}}\text{= 19.3 ± 0.5}\text{and}\text{19.2 ± 0.3}\text{kG at}\text{1.65}\text{K}$, respectively). The transition involves flopping of the spins within the linear chains while the inter-chain order (the “triangular configuration”) is preserved. The low values of H_s?:; imply a small anisotropy parameter (D = -0.05 cm^-1).     

Magnetic susceptibility and valency state in Sm3S4

The lack of pronounced temperature dependence in the magnetic susceptibility of Sm₃S₄ rules out a magnetic ground state for Sm ions. Comparison with semiconducting and metallic phases of SmS suggest the presence of one Sm²⁺ ion for two non-integral valency Sm ions.     

Spin-phonon interactions near the one-dimensional antiferromagnetic ordering in CsNiCl3

The velocity of 10 MHz and 27 GHz longitudinal phonons propagating along the c-axis in the one-dimensional antiferromagnet CsNiCl₃ has been measured using ultrasonic and Brillouin light scattering techniques, respectively. An anomalous change in phonon velocity near the one-dimensional magnetic ordering temperature due to the spin-phonon interaction has been observed in both cases.     

59Co nuclear magnetic resonance in antiferromagnetic CsCoCl3

The ⁵⁹Co NMR in a CsCoCl₃ single crystal has been observed by the spin echo method at 4.2 K. The obtained spectrum is composed of seven distinct lines split by the nuclear-quadrupole interaction. The frequency of the central (± $\text{1}\text{2}$ ? ± $\text{1}\text{2}$) transition 502.08±0.05 MHz corresponds to the hyperfine field of 499.38 ± 0.05 kOe, which agrees well with the calculated value. Due to the interaction of the nucleus with the electronic moment induced by the external field, a shift as large as 18% was observed for the nuclear g-factor.     

Optical amplification properties of Dy3+-doped Gd2SiO4, Lu2SiO5 and YAl3(BO3)4 single crystals

Comparative investigation of the optical amplification properties of dysprosium doped Gd₂SiO₅, Lu₂SiO₅ and YAl₃(BO₃)₄ single crystals was performed in a pump-and-probe experiment. High power laser pulses at 475 nm were used as the pump source in order to strongly populate the ⁴F_9/2 level of the Dy³⁺ ions due to ground state absorption. Low signal beam cw radiation at 574 nm was used as the probe beam to stimulate the emission associated with the ⁴F_9/2→⁶H_13/2 electronic transition of the Dy³⁺ ions. The process was modelled as a three levels system, and their populations were analysed and simulated in order to study the gain dynamics. Positive optical gain was observed and compared in these crystals. These results confirmed that among the systems studied the Dy³⁺-doped YAl₃(BO₃)₄ single crystal can be considered as a good candidate to develop an optical amplifier employing the ⁴F_9/2→⁶H_13/2 transition at around 574 nm which is the first step to consider as laser active media.     

The preparation and characterization of the cobalt skutterudites CoP3, CoAs3 and CoSb3

Single crystals of the cobalt skutterudites CoP₃, CoAs₃ and CoSb₃ have been prepared by the chemical vapor transport technique using chlorine as the transport agent. Chemical analysis and density measurements were used to determine accurately the stoichiometry of these crystals. Physical properties of chemically pure single crystals were obtained by X-ray diffraction, magnetic susceptibility and electrical measurements. CoP₃ is a diamagnetic semiconductor with an optical band gap of 0.45 eV. CoAs₃ and CoSb₃ are also diamagnetic and show an increase in their resistivity as a function of increasing temperature. In addition, they do not give any measurable absorption edge but absorb radiation at all frequencies from 0.4 to 4.3 eV.