Dynamics of H2O molecules in ferroelectric K4Fe(CN)6 · 3H2O

The infrared spectrum of potassium ferrocyanide trihydrate has been recorded both in the para and ferroelectric phases. From a combined study of the IR and Raman spectra, it is concluded that there are two sets of water molecules present in the lattice, one set being involved in stronger hydrogen bonding than the other. The ferroelectric transition appears to be associated with an ordering of the water dipoles.     

Growth and vibrational spectroscopic studies of strontium tartrate (C4H4O6Sr): a nonlinear optical single crystal

The nonlinear optical crystal strontium tartrate (SrT) was grown by the gel method. The vibrational spectra were recorded to determine the symmetries of molecular vibrations. The microhardness of the crystal was also tested. The observed, infrared (IR) bands were also assigned and discussed. The optical transmission spectral study was also carried out. The nonlinear property is confirmed. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman and infrared spectral studies of [C(NH2)3]2MII(H2O)4(SO4)2, MII = Mn,Cd and VO

The Raman and FTIR spectra of three metal guanidinium sulfates, [C(NH₂)₃]₂M^II(H₂O)₄(SO₄)₂, (M^II = Mn, Cd and VO), are recorded. The observed spectral bands are assigned in terms of the fundamental modes of vibration of the guanidinium ions, sulfate groups and water molecules. The appearance of the sulfate tetrahedra's ν₁ and ν₂ modes in the IR spectra and the partial lifting of the ν₄ mode in the Raman spectra indicate the distortion of the SO₄²⁻ tetrahedra in the structure, so that its symmetry is lowered from T_d to C₁. The geometry of the sulfate group in guanidinium vanadyl sulfate does not deviate much from that of the average sulfate group. The distortion of the SO₄ tetrahedra is stronger in GuCds than in GuMnS. The CN₃ group in the guanidinium ion is planar (D_3h point group) in GuCdS and GuMnS, whereas it is lowered in the vanadyl compound. Furthermore, the spectral analyses show the presence of weak hydrogen bonds in the structures. Copyright © 2007 John Wiley & Sons, Ltd.     

Neutron diffraction study of (NH4I)0.73(KI)0.27

Powder and single crystal neutron diffraction experiments were performed on (NH₄I)_0.73(KI)_0.27 and provide experimental evidence for the occurence of a new phase below 63K. This ε phase has trigonal symmetry (space group R3m) and was, so far, not observed in the ammonium halides. It can be characterized by an almost undistorted NaCl lattice, with two in-equivalent NH₄ sites of the four NH₄ molecules per unit cell. The NH₄ group at the trigonal axis (the former cubic <111> axis) is almos perfectly tetrahedral. The other three NH₄ molecules are 0.18 Å off center and exhibit C_3v symmetry with the polar axis along the remaining three body diagonals. Hence, this ε phase reveals a complex dipolar order with a residual moment along the trigonal axis.     

Neutron diffraction study of (NH4I)0.73(KI)0.27

Powder and single crystal neutron diffraction experiments were performed on (NH₄I)_0.73(KI)_0.27 and provide experimental evidence for the occurence of a new phase below 63K. This ε phase has trigonal symmetry (space group R3m) and was, so far, not observed in the ammonium halides. It can be characterized by an almost undistorted NaCl lattice, with two in-equivalent NH₄ sites of the four NH₄ molecules per unit cell. The NH₄ group at the trigonal axis (the former cubic <111> axis) is almos perfectly tetrahedral. The other three NH₄ molecules are 0.18 Å off center and exhibit C_3v symmetry with the polar axis along the remaining three body diagonals. Hence, this ε phase reveals a complex dipolar order with a residual moment along the trigonal axis.     

Neutron diffraction and Mössbauer study on FeGa x Cr2−x S4

Ga doped sulphur spinel FeGa _x Cr_2?x S₄ (x = 0.1 and 0.3) have been studied with X-ray, neutron diffraction, and Mössbauer spectroscopy. Rietveld refinement of X-ray, neutron diffraction, and Mössbauer spectroscopy lead to the conclusion that the samples are in inverse spinel type, where most Ga ions are present at octahedral site (B). The neutron diffractions on FeGa _x Cr_2?x S₄ (x = 0.1) above 10 K show long range interaction behaviors and reveal a ferrimagnetic ordering, with the magnetic moment of Fe²⁺(?3.45 μ_B) aligned antiparallel to Cr³⁺ (+2.89 μ_B) at 10 K. Fe ions migrate from the tetrahedral (A) site to the octahedral (B) site with an increase in Ga substitutions. The electric quadrupole splittings of the A and B sites in Mössbauer spectra give direct evidence that Ga ions stimulate an asymmetric charge distribution of Fe ions in the A site.     

Vibrational analysis of NaM2OH(H2O)(MoO4)2/D2O [M=Ni,Zn]

The infrared and Raman spectra of NaNi₂OH(H₂O)(MoO₄)₂ and NaZn₂OH (H₂O)(MoO₄)₂ and their partially deuterated analogues are recorded and analysed on the basis of vibrations of MoO ₄ ²⁻ tetrahedra and H₂O molecules. The MoO ₄ ²⁻ groups are found to be more distorted in NaNi₂OH(H₂O)(MoO₄)₂ than in the other compound. Bands indicating the presence of H₃O⁺ ions are not observed in NaZn₂OH(H₂O)(MoO₄)₂ ruling out the possibility of the formulation of NaZn₂OHO(MoO₃OH)₂. Hydrogen bonds of medium strength are present in both the compounds.     

Zinc (tris) thiourea sulphate (ZTS): A single crystal neutron diffraction study

The crystal structure of ZTS has been determined by neutron diffraction with a finalR-value of 0.026. Using the structural parameters, the contributions from the structural groups to the linear optical susceptibility and linear electro-optic coefficients have been evaluated. Results showed a significant contribution from the hydrogen bonds in the structure.     

Neutron diffraction study of multipole order in light rare-earth hexaborides

Multipole interactions are known to play a central role in the unconventional properties of light rare-earth hexaborides and especially of CeB₆. Substituting Pr at the Ce sites has the effect of enhancing exchange interactions and changing the symmetry of the local 4f charge distribution, while suppressing the octupole moment. The (T, H) magnetic phase diagrams of the Ce _x Pr_{1 − x} B₆ compounds display a large variety of ordered phases involving magnetic and/or charge degrees of freedom. Here we focus on the compound Ce_0.7Pr_0.3B₆, which is located slightly beyond the Pr concentration where the antiferroquadrupolar phase of pure CeB₆ is suppressed in zero field. The different magnetic structures have been characterized by neutron diffraction and their origin is discussed in connection with recent non-resonant X-ray results by Tanaka et al.      

中子衍射分析时效处理对镍基单晶高温合金相结构的影响

采用φ振荡和φ固定两种数据采集模式的中子衍射实验结果表明较高的时效温度对消除枝晶最有效,微应变(晶粒区域间的变形不协调性)主要存在于γ'相.利用中子衍射结合扫描电子显微镜对合金的微观组织形貌进行了细致观察,给出了时效温度和时间对γ'相的影响状况,超晶格测量发现了γ'相晶粒之间出现的独特取向差.由不同晶面的中子衍射结果判断时效后合金出现了轻微的四方对称性(a < c)畸变,对这种畸变起主要作用的是基体相.实验结果同时证实了不同方向的应变差异,因而为筏化驱动模型的定量 关键词： 单晶高温合金 中子衍射 超晶格 时效处理     

Mössbauer study of (NH4)2FeCl5.H2O

We report Mössbauer data between 1.3K and 300K, with applied fields of up to 10T at 4.2K, of (NH₄)₂FeCl₅.H₂O. We found no evidence of a reported structural phase change just above T_N(～7.3K), nor did we see any spin reorientation just below T_N. The V₂₂ axis was found to be in the ac plane at ～17° to the a axis and the spins, below T_N, were found to be approximately parallel to the a axis. The spin reorientation in applied field occured gradually between 0T and 5T; this and previously reported susceptibilty data have led to the hypothesis that (NH₄)₂FeCl₅.H₂O is a weak ferromagnet.     

Mössbauer study of (NH4)2FeCl5·H2O

Mössbauer spectra of the compound (NH₄)₂FeCl₅·H₂O have been studied as a function of temperature. Two phase transitions are observed in the temperature range between 7 K and 9 K. The transition at 9 K is structural and presents an unusually high thermal hysteresis. AroundT=8 K the substance orders magnetically and different Fe³⁺ contributions are present.     

Observation of stimulated Raman scattering in polar tetragonal crystals of barium antimony tartrate trihydrate,Ba[Sb2((+)C4H2O6)2]·3H2O

The non‐centrosymmetric polar tetragonal (P 4₁) barium antimony tartrate trihydrate, Ba[Sb₂((+)C₄H₂O₆)₂]·3H₂O, was found to be an attractive novel semi‐organic crystal manifesting numerous χ ⁽²⁾‐ and χ ⁽³⁾‐nonlinear optical interactions. In particular, with picosecond single‐ and dual‐wavelength pumping SHG and THG via cascaded parametric four‐wave processes were observed. High‐order Stokes and anti‐Stokes lasing related to two SRS‐promoting vibration modes of the crystal, with ω_SRS1 ≈ 575 cm^?1 and ω_SRS2 ≈ 2940 cm^?1, takes place. Basing on a spontaneous Raman investigation an assignment of the two SRS‐active vibration modes is discussed.

     

Structure determination of Ls-threonine by neutron diffraction

The structure of the aminoacid, L_s-threonine [NH ₃ ⁺ CH(CHOHCH₃)COO^?], space groupP2₁2₁2₁,a=13.630(5),b=7.753(1),c=5.162(2) Å,z=4, has been determined from neutron diffraction data using direct methods. The intensities of 1148 neutron Bragg reflections were measured from a single crystal. The structural parameters were refined by the method of least squares using anisotropic temperature factors. The finalR(F ²) is 0.068. The structure was also refined from the x-ray data of Shoemakeret al (1950J. Am. Chem. Soc. 72 2328); there is good agreement between the two sets of heavy atom parameters. The parameters of hydrogen atoms are of course more precisely determined in our neutron study. The molecular conformation and the hydrogen bonding scheme are discussed. Weighted average values of bond distances and angles from 14 aminoacid structures with ionized carboxylic groups studied by neutron diffraction at Brookheven and Trombay are also presented.     

Chlorine-35 nuclear quadrupole resonance and phase transitions in (4ClC6H4NH3)2MnCl4, (4-Cl6H4NH3)2CUCl4, and (4-ClC6H4NH3)2CUBr4

The temperature dependence of the ³⁵Cl NQR frequencies of 4-chloroanilinium cations in (4-ClC₆H₄NH₃)₂MnCl₄, (4-ClC₆H₄NH₃)₂CuCl₄, and (4-ClC₆H₄NH₃)₂CuBr₄ was studied over a wide range of temperature. For the two copper(II) complexes, magnetic susceptibilities were measured below approximately 20 K. The lattice constants of these isomorphous orthorhombic crystals were determined. Magnetic phase transitions to three-dimensionally long-range-ordered states were found at 40, 8, and 13 K for the respective complexes. Additional structural phase transitions were also found at higher temperatures for all of the complexes studied. Magnetic properties in the ordered state and the nature of both types of phase transitions are discussed.     

Proton ENDOR of VO(H2O)5 2+ in Mg(NH4)2(SO4)2)26H2O

ENDOR measurements at 25 K have been used to determine the hyperfine coupling tensors for all ten protons in the VO(H₂O)₅ ²⁺ ion in single crystals of Mg(NH₄)₂(SO₄)₂6H₂O. The traceless components of all the tensors are close to axial and their use in a point dipole treatment enables a very plausible geometrical model of the complex ion to be constructed. Six of the protons in the equatorial water molecules have substantial positive isotropic couplings and it is suggested that these reflect the direct admixture of hydrogen 1s components into the singly occupied orbital.     

中子衍射法研究单晶镍基高温合金热机械疲劳引起的应力和晶格错配

采用中子衍射法对热机械疲劳后的单晶镍基高温合金样品内部中心点进行了实验测量,数据处理采用了双相叠加峰和单峰分析两种方法,计算得到了样品材料的宏观等效应力、应力偏量、γ相和γ′相的等效应力和晶格错配度等.实验结果表明,两种分析方法得到的宏观等效应力基本一致.在热机械疲劳循环100周出现最大宏观等效应力和应力偏量,此时位错等微缺陷达到饱和,偏离中心点处γ′相应力减小显著;在热机械疲劳开始阶段负错配度明显减小,随循环周次增多基体塑性应变累积又使负错配度以每次81×10^-6的速度逐渐线形增大. 关键词： 中子衍射 单晶高温合金 等效应力 应力偏量     

High-pressure dielectric studies of a novel hydrogen-bonded ferroelectric (NH4)2H2P2O6

The hydrostatic pressure effect on the dielectric properties of (NH₄)₂H₂P₂O₆ ferroelectric crystal was studied for pressures from 0.1 MPa to 360 MPa and for temperatures from 100 to 190 K. The pressure–temperature phase diagram obtained is linear with increasing pressure. The paraelectric–ferroelectric phase transition temperature decreases with increasing pressure with the pressure coefficient dT_c/dp=?5.16×10^?2 K MPa^?1. Additionally, the pressure dependences of Curie–Weiss constants for the crystal in paraelectric (C₊) and ferroelectric (C_?) phases are evaluated and discussed. The possible mechanism of paraelectric–ferroelectric phase transition is also discussed.