Glass formation and structure of glasses in the ZnO―Bi2O3―WO3―MoO3 system

The glass formation region in the ternary ZnO―Bi₂O₃―WO₃ system is determined by melt quenching technique (cooling rates 10¹-10² K/s). New original glasses are obtained in a narrow concentration range with high WO₃ content (60-75 mol%). Homogeneous glasses of the composition (100 − x)[0.2ZnO·0.3Bi₂O₃·0.5WO₃]xMoO₃, were obtained between 20 and 60 mol% MoO₃. Characterization of the amorphous samples was made by x-ray diffraction (XRD), differential thermal analysis (DTA) and infrared spectroscopy (IR). The thermal stability of glasses decreases with the increasing of MoO₃ content. The glass transition temperature, T_g, varies between 340-480 °C, while the crystallization temperature, T_x, varies between 388-531 °C. The tungstate glasses possess higher crystallization temperature (T_x over 500 °C) in comparison with the other vanadate and molybdate non-traditional glasses. The glass network is realized by transformation of three-dimensional structure of WO₃ into a layered one, consisting mainly of WO₆ units. We supposed that the network of quaternary glasses is built up by MoO₄, MoO₆ and WO₆. At low concentration ZnO and Bi₂O₃ facilitate the disorder in the supercooled melts, while at high concentration stimulate crystallization processes. These oxides belong to the intermediate ones.     

Structural and magnetic behaviour of lead-bismuthate glasses containing rare earth ions

Lead-bismuthate glasses containing rare earth ions in the xR₂O₃(1 − x)[3Bi₂O₃⋅ PbO] (R = Nd, Eu, Er and Gd), xCeO₂(1 − x)[3Bi₂O₃⋅ PbO] and xTb₄O₇(1 − x)[3Bi₂O₃⋅ PbO] vitreous systems with x up to 0.25 were prepared and investigated by density, IR spectroscopy and magnetic susceptibility measurements. Density data show that the gradual addition of the rare earth ions leads not only to a simple incorporation of the rare earth ions in the host glass matrix but also generates structural changes of the vitreous matrix. FTIR data permitted to determine the Bi³⁺/Bi⁶⁺ ratio of the samples and to follow the compositional evolution of the structural changes for the studied systems. Magnetic susceptibility data show that the magnetic rare earth ions appear as isolated species for low rare earth oxide contents (x ≤ 0.03 ÷ 0.05) and as both isolated and magnetically coupled species for higher contents. All the magnetic rare earth ions present a very accentuated clustering tendency. Some of the studied rare earth ions appear in the host glass matrix in a single valence state (neodymium, gadolinium, and erbium), namely the 3+ one. Other rare earth ions appear in two valence states (i.e., cerium, europium and terbium), but the 3+ one is the most stable.     

ZnGeP2单晶生长温场研究

根据ZnGeP2(ZGP)晶体的生长特性,自行设计组装了三段式独立控温生长炉,优化了温场分布.采用改进的垂直布里奇曼法成功生长出外观完整、无裂纹的ZGP单晶体,尺寸达15 mm×35 mm.对晶体进行解理实验和X射线衍射分析,发现ZGP晶体易沿(101)面解理,其回摆峰尖锐无劈裂.对未经退火处理的晶片进行红外透过率测试,在2～12 μm波段内红外透过率达45;以上.研究结果表明所设计的温场适合于ZGP单晶生长,生长出的ZGP晶体完整性好、质量较高.     

Vibrational, EPR and optical spectroscopy of the Cu doped glasses with (90-x)TeO2-10GeO2-xWO3 (7.5 ≤ x ≤ 30) composition

Infrared, EPR and optical absorption studies on (90-x)TeO₂-10GeO₂-xWO₃ (7.5 ≤ x ≤ 30) glasses containing Cu²⁺ spin probe have been carried out. The Infrared spectral studies show that the structure of glass network consists of [TeO₄], [TeO₃]/[TeO_3 + 1], [WO₄], [WO₆] and [GeO₆] units in the disordered manner. Physical parameters such as density (ρ), molar volume (V_m), oxygen packing density (OPD), oxygen molar volume (V_o), optical basicity (Λ), oxide ion polarizability (α_O²⁻), inter ionic distances and the concentration of ions per unit volume of Te, Ge, W, Cu and O have been determined. The spin-Hamiltonian parameters (g_||, g_⊥ and A_||) of Cu²⁺ ions in the present glasses have been estimated from EPR spectra at 300 K. Bonding parameters such as α², β₁², β², Γ_σ, and Γ_π have been calculated from both optical absorption and EPR data. The observed variations in spin-Hamiltonian parameters and bonding parameters have been correlated to the structural modifications due to the WO₃ incorporation into the TeO₂ glass network at constant 10 mol% GeO₂ content.     

The importance of inter-molecular forces in crystal structure analysis: Solid state study of the diag-to-lat isomerization of (η5-C5H4Me)Re(CO)2Br2

Single crystal X-ray structures of diag and lat-(⁵-C₅H₄Me)Re(CO)₂Br₂ have been determined. The diag form crystallizes in the triclinic space group , a = 6.751(2), b = 8.537(1), c = 9.758(1) Å = 96.70(1), = 93.15(2), = 104.96(2)°, V = 534.8(2) ų, Z = 2. The lat form is monoclinic, P2₁/c, a = 11.820(1), b = 7.133(1), c = 12.924(1) Å = 98.278(8)°, V = 1078.2(2) ų, Z = 4. The unit cell volumes (per Z) of the two isomers differ by ca 1%. Molecular modelling reveals an energy difference between the two isomers of 1 kJ mol^–1 or less. The XRD powder diffraction patterns for the lat isomer produced by crystallization from solution or prepared by thermal isomerization are identical. The evidence thus suggests that the solid state isomerization reaction is a novel example of a reaction which yields a molecular structure determined by crystal packing forces.     

Vibrational spectra,electronic properties and effect of alkyl chain length on chemical stability of nematogens – A comparision using DFT and HF methods

The vibrational spectra of lower homologous series of nematogenic p-n-alkylbenzoic acids (nBAC) with 4 (4BAC) and 5 (5BAC) carbon atoms in the alkyl chain have been investigated using the Density Functional Becke3-Lee-Yang-Parr (B3LYP) level with the basis set 6–31++G(d.p) and Hartree Fock (HF) with the same basis set. The observed vibrational spectra has been resolved and assigned in detail for comparision with both the molecules. These results indicate that DFT and HF values are slightly different at both the level. A comparision of electronic properties such as HOMO (E_HOMO), LUMO (E_LUMO) energies, energy gap (E_g), ionization potential (I), electron affinity (A), electro negativity (χ), chemical hardness (η), electronic chemical potential (μ), electrophilicity index (ω), and softness (S) has been made. It has been observed that decrement occurred in the energy band gap value of isolated molecule with increment in alkyl chain length. This provides valuable information regarding the stability of liquid crystal materials.     

A quasi-layer structure of trinuclear molybdenum(IV) cluster, [Mo3S7(S2CNEt2)3]I·S8

The title compound, [Mo₃(₃-S)(-S₂)₃(S₂CNEt₂)₃]I·S₈, was obtained by solid state reaction of (NH₄)₂MoS₄, Et₂NCS₂Na, and Et₄NI at low heating temperature and crystallizes in space group P with a = 13.572(3), b = 13.813(4), c = 13.239(3) Å, = 92.63(3), = 100.15(3), = 117.89(2)°, V = 2136(2) ų, and D _calc. = 2.08 g/cm³ for Z = 2. The structure reveals that it consists of a trinuclear Mo cluster molecule, [Mo₃S₇(S₂CNEt₂)₃]I, and one S₈, which are connected to form a quasi-layer structure by the interaction between S₈ and the S atoms of the cluster molecule.