Measurement of electro-optic coefficients of low-symmetry crystal YbCa4O(Bo3)3

In this paper, we report on all the electro-optic coefficients of the low-symmetry crystal YbCa₄O(BO₃)₃ measured by the interferometric method. The new sample orientations, which have not been reported so far, have been used for measuring the skew electro-optic coefficients γ₅₁, γ₅₃, γ₄₂ and γ₆₂ independently. The results obtained are γ₁₁=0.6, γ₂₁=0.4, γ₃₁=0.3, γ₁₃=0.3, γ₂₃=0.2, γ₃₃=2.2, γ₅₁=0.9, γ₅₃=4.1, γ₄₂=0.8 and γ₆₂=0.4×10⁻¹² m/V.     

The 3ν3 overtone bands of UF6 and UF6

The absorption specta of CO laser radiation by 3ν₃ overtone bands of ²³⁸UF₆ and ²³⁵UF₆ has been measured using photoacoustic spectroscopic techniques. For the two temperatures 250 K and 290 K, measured absorption coefficients and cross-sections of the 3ν₃ band of ²³⁵UF₆ are reported for the first time.     

Effect of γ-radiation on the phase transition temperature of Li0.5(NH4)0.5SO4

Polycrystalline lithium-ammonium sulphate samples were subjected to X-ray diffraction analysis for determining the lattice parameters of the prepared mixed crystals. The compositions of the samples were determined using X-ray microanalysis.

The Li_0.5(NH₄)_0.5SO₄ samples were irradiated with different doses of γ-radiation in order to investigate the effect of this ionizing radiation on the phase transition temperatures T_c1 and T_c2. The temperature dependence of the d.c. resistivity ρ_d.c. and dielectric constant of irradiated samples showed (i) a shift of T_c1 to higher temperatures; (ii) a shift of T_c2 to lower temperatures; and (iii) the appearance of a new anomaly near 128°C at moderately high γ-doses. The mechanisms giving rise to this behaviour are discussed.     

Li2K(IO3)3与Li2NH4(IO3)3的晶体结构

本文用X射线粉末法测定了Li₂K(IO₃)₃与Li₂NH₄(IO₃)₃的晶体结构和原子参数。发现Li₃K(IO₃)₃,Li₂NH₄(IO₃)₃与Li₂Rb(IO₃)₃同晶型,属单斜晶系,空间群为P2₁/α,每个单胞含有四个化合式量。室温的点阵常数分别为α=11.198?,b=11.046?,c=8.254?,β=111.53°,及α=11.327?,b=11.078?,c=8.341?,β=111.87°。讨论了二元化合物的形成与离子半径的关系。 关键词：     

Low-temperature AC conductivity of Bi2Sr2CaCu2O8+δ

We report measurements of anamolously large dissipative conductivities, σ₁, in Bi₂Sr₂CaCu₂O_8+δ at low temperatures. We have measured the complex conductivity of Bi₂Sr₂CaCu₂O_8+δ thin films at 100–600 GHz as a function of doping from the underdoped to the overdoped state. At low temperatures there exists a residual σ₁ which scales with the T=0 superfluid density as the doping is varied. This residual σ₁ is larger than the possible contribution to σ₁ from a thermal population of quasiparticles (QP) at the d-wave gap nodes.     

Spectral intensities in the ν1 band of NH3

Intensities have been measured for individual transitions in the Q and R branches of the ν₁ band of NH₃ using a difference-frequency laser spectrometer. The data yield an integrated band strength of S⁰_v=219.36±1.03 cm^-2/MPa at 297 K, corresponding to a transition moment of μ_v = 8.535(20) × 10^-32 C·m, and a Herman-Wallis correction factor, (1 + _jm)², where _j = 0.0209(20). The intensities of a few lines for K 7 were noticeably perturbed by a perpendicular Coriolis interaction with 2ν₄ (E, L = 2), so were excluded from the fit. A small sample of ν₃ band lines occurring in the ν₁ band scans also yields a rough estimate of the ν₃ band intensity with evident irregular perturbations.     

Mössbauer investigations on Np3S5

The 59.5 keV Mössbauer resonance of ²³⁷Np has been measured in Np₃S₅ at 77 and 4.2 K. At 77 K, two different quadrupolar splittings are observed. The first one (δ₁ = −5(1) mm sec⁻¹/NpAl₂) is assigned to the Np⁴⁺ ions and the second one (δ₂ = 28(1) mm sec⁻¹/NpAl₂) is assigned to the Np³⁺ ions. At 4.2 K the spectrum gives a ratio of areas S(Np³⁺)/S(Np⁴⁺) of 2.0. These results clearly confirm the crystallographic data of this mixed-valence material.     

A 62 K superconductor with an original structure: Sr4−xBaxTlCu2CO3O7

A new superconductor with an original structure, Sr_4−xBa_xTlCu₂CO₃O₇ has been isolated for 1≤x≤2. It crystallizes in a A-type space group with a=3.84 Å≈a_p, b≈8 × a_p, c≈17.0 Å. The HREM study of this new curprate shows that it derives from the Tl_0.5Pb_0.5Sr₄Cu₂CO₃O₇ structure by a shearing mechanism. Indeed, it can be described as ribbons of the latter structure, four octahedra thick, shifted c/2 with respect to each other. It results in infinite single perovskite layers waving along the (001) plane and connected through flat mixed layers [(TIO)₄(CO)₄]∞. This oxycarbonate can also be described as a 1201-type structure in which the [TIO]∞ layers are replaced by mixed [(TIO)₄(CO)₄]∞ layers. The susceptibility measurements show that this cuprate exhibits a significantly higher critical temperature than the 1201-cuprates. The T_{c onset} of the synthesized phase is 56 K and it can be increased up to 62 K by hydrogen annealing; in the same way, one observes a large Meissner volume fraction of 35% at 4.2 K.     

Effect of lead addition to Bi-based 2222 superconducting cuprates Bi2-xPbxSr2(Y, Ce)2Cu2O10+δ

Bi_2-xPb_xSr₂(Y, Ce)₂Cu₂O_10+δ, a new family of lead containing Bi-2222 compounds has been synthesized and effects of annealing in high pressure of oxygen studied. Lead-free Bi₂Sr₂(Y, Ce)₂Cu₂O_10+δ synthesized under flowing oxygen is known to be non-superconducting, but annealing under high oxygen pressure (100 bar) at 500°C, induced superconductivity with T_c=25 K. On substitution of lead (x>0.4), the superconductivity appears even in samples synthesized under flowing oxygen (1 bar). T_c increases with oxygen annealing pressure for all compositions, and it also increases with Pb content at a given oxygen pressure. These findings are discussed.     

Study on the superconducting composite material formation in the system Bi2Sr2CaCu2O8+x/Al-containing phases

Phase evolution in the Bi---Sr---Ca---Cu---Al---O system was studied. Two Al-containing phases BiSr_1.5Ca_0.5Al₂O_z and (Sr_1−xCa_x)₃Al₂O₆ (x = 0.4 − 0.45) were determined to be chemically compatible with Bi_2.18Sr₂CaCu₂O_8+x (Bi-2212) at temperatures of the samples processing. The phase equilibria in the title system were investigated above the solidus temperature. The BiSr_1.5Ca_0.5Al₂O_z was found to be in equilibrium only with the melt and the (Sr_1−xCa_x)₃Al₂O₆ phase. This latter aluminate equilibrated with Ca,Sr cuprates, CaO, the Cu-free phase, and the liquid. The melting and solidification in Bi-2212, doped with the aluminate, corresponded to the reversible reaction Bi-2212 + BiSr_1.5Ca_0.5Al₂O_z ↔ (Sr_1−xCa_x)₃Al₂O₆ + liquid. Two sets of superconducting composite materials with initial compositions Bi-2212 + nBiSr_1.5Ca_0.5Al₂O_z and Bi-2212 + m(Sr_1−xCa_x)₃Al₂O₆ were prepared by solidification from the partial melt. The former material was composed mostly of large Bi-2212 lamellas separated by the BiSr_1.5Ca_0.5Al₂O_z phase, which destroyed superconducting links between Bi-2212 grains. The latter material consisted of a Bi-2212 polycrystalline matrix with high concentration of small (ca. 3 μm) grains of (Sr_1−xCa_x)₃Al₂O₆ imbedded in Bi-2212 lamellas. The Bi-2212 + m(Sr_1−xCa_x)₃Al₂O₆ materials displayed a trend to enhance flux pinning at T = 60 K with the increase of aluminate phase content.     

NMR study of monomethylammonium cation in (CH3NH3)5Bi2Cl11 ferroelectric polycrystal

Spin-lattice relaxation times T₁ and T_1ρ are determined for protons in three polycrystals (CH₃NH₃)₅Bi₂Cl₁₁, (CD₃NH₃)₅Bi₂Cl₁₁ and (CH₃ND₃)₅Bi₂Cl₁₁. The temperature dependencies of the relaxation times obtained for (CH₃NH₃)₅Bi₂Cl₁₁ and (CD₃NH₃)₅Bi₂Cl₁₁ are interpreted as a result of correlated motions of the three-proton groups of the monomethylammonium cation. The minimum of the T_1ρ relaxation time is explained as a result of the oscillations of the symmetry axis of the whole cation.     

铁电单晶(KxNa1-x)0.4(SryBa1-y)0.8Nb2O6的光学性质和线性电光效应

本文介绍铁电单晶(K_xNa_1-x)_0.4(Sr_yBa_1-y)_0.8Nb₂O₆的光学性质和线性电光效应的测量。实验结果表明,这种晶体具有较大的光学双折射,透光范围由4000?到5.6μm。晶体具有低的线性电光调制的半波电压,其电光调制价值指数n₀³·γ_c高达730×10 关键词：     

Structural and lithium intercalation studies of Mn(0.5−x)CaxTi2(PO4)3 phases (0≤x≤0.50)

Materials from the Mn_(0.5−x)Ca_xTi₂(PO₄)₃ (0≤x≤0.50) solid solution were obtained by solid-state reaction in air at 1000 °C. Selected compositions were investigated by powder X-ray diffraction analysis, ³¹P nuclear magnetic resonance (NMR) spectroscopy and electrochemical lithium intercalation. The structure of all samples determined by Rietveld analysis is of the Nasicon type with the R space group. Mn²⁺/Ca²⁺ ions occupy only the M1 sites in the Ti₂(PO₄)₃ framework. The divalent cations are ordered in one of two M1 sites, except for the Mn_0.50Ti₂(PO₄)₃ phase, where a small departure from the ideal order is observed by XRD and ³¹P MAS NMR. The electrochemical behaviour of Mn_0.50Ti₂(PO₄)₃ and Mn_(0.5−x)Ca_xTi₂(PO₄)₃ phases was characterised in Li cells. Two Li ions can be inserted without altering the Ti₂(PO₄)₃ framework. In the 0≤y≤2 range, the OCV curves of Li//Li_yMn_0.50Ti₂(PO₄)₃ cells show two main potential plateaus at 2.90 and 2.50–2.30 V. Comparison between the OCV curves of Li//Li_(1+y)Ti₂(PO₄)₃ and Li//Li_yMn_0.50Ti₂(PO₄)₃ shows that the intercalation occurs first in the unoccupied M1 site of Mn_0.50Ti₂(PO₄)₃ at 2.90 V and then, for compositions y>0.50, at the M2 site (2.50–2.30 V voltage range). The effect of calcium substitution in Mn_0.50Ti₂(PO₄)₃ on the lithium intercalation is also discussed from a structural and kinetic viewpoint. In all systems, the lithium intercalation is associated with a redistribution of the divalent cation over all M1 sites. In the case of Mn_0.50Ti₂(PO₄)₃, the stability of Mn²⁺ either in an octahedral or tetrahedral environment facilitates cationic migration.     

EPR evidence of local lattice mode in K3H(SO4)2 and Rb3H(SO4)2 fast-proton conductors

The observation of an anomalous temperature dependence of Mn²⁺ EPR spectra linewidth and nonaxial crystal-field parameter in K₃H(SO₄)₂ and Rb₃H(SO₄)₂ allows one to suggest the presence of “local mode” predicted by Yamada (Ferroelectrics 170 (1995) 23). The activation energy for this kind of excitation was found and equals 11.3 (0.5) and 7.4 (0.3) meV for Mn²⁺ doped K₃H(SO₄)₂ and Rb₃H(SO₄)₂, respectively.     

A new type oscillatory phenomenon in the magnetotransport of θ-(BEDT-TTF)2I3

A new type oscillatory magnetotransport phenomenon has been observed in θ-type crystals of (BEDT-TTF)₂I₃ at temperatures below 6 K and in the magnetic field above 3 T. The oscillation appears when the magnetic field of a fixed strength is rotated from the direction normal to the conductive two dimensional plane to a direction parallel to the plane. The period of the oscillation is described by an equation tan (θ_min)=sN (s=0.39, N=0, 1, 2, 3,…), where θ_min is the angle giving the position of the trough of the oscillation. The amplitude of the oscillation is primarily determined by the magnetic field component normal to the conductive plane. It is related to the temperature through the change in the resistivity ₀.     

正磷酸盐晶体Ba3(PO4)2和Sr3(PO4)2高温拉曼光谱研究

测量了碱土金属正磷酸盐Ba₃(PO₄)₂和Sr₃(PO₄)₂常温及高温拉曼光谱, 对拉曼振动模式进行指认, 并分析了晶体拉曼振动光谱及晶体结构在高温下的变化. 在温度升高的过程中, 拉曼振动频率向低频移动且振动峰宽度展宽, 晶体中的P-O平均键长随温度升高而变长, 但O-P-O的键角并未发生变化. 晶体在900 ℃以下无结构相变发生. 关键词： 3(PO₄)₂和Sr₃(PO₄)₂')" href="#">Ba₃(PO₄)₂和Sr₃(PO₄)₂ 高温拉曼光谱 振动模式 高温结构     

LiIO3-Zn(IO3)2 赝二元系的研究

用固态粉末烧结法配制样品,用X射线衍射及差热分析等方法研究并测定了LiIO₃-Zn(IO₃)₂赝二元系的相图。该二元系内存在一新相LiZn(IO₃)₃。它有较大的倍频效应,具有离子导电性。用自编的由粉末衍射数据求单斜晶系的点阵参数的计算机程序成功地求出了该化合物的点阵常数。经过进一步修正,确定它属于正交晶系,α=8.08l?,b=8.729?,c=11.595?,z=4。并确定了化合物存在的成分范围和条件。 关键词：     

Magnetic properties of TmFeO3 and TmGa0.13Fe0.87O3 orthoferrites

The magnetization σ_c has been observed to depend strongly on temperature and biasing field in the Γ₄-phase. Two families of σ_c (T) occur corresponding to the poly-domain (H < 200 Oe), and mono-domain (H > 200 Oe) states of the samples. This was proved by observation of domain structures in these samples. In addition to the maximum due to the second-order phase transition Γ₂-Γ₄, we have revealed a maximum in the susceptibility curves _Xc(T) at the high-temperature point of phase transition. The second maximum strongly depends on the biasing field value. Domain structure behaviour in that temperature range, and in various external fields, allowed us to suggest that there exists a relation between this maximum and the shifting processes of domain boundaries, which create a significant susceptibility along the c-axis.     

真空紫外光激发下Ce3+、Tb3+激活的BaCa2(BO3)2的发光性质

利用XRD、VUV及UV光谱等方法对Ce³⁺、Tb³⁺离子掺杂以及Ce³⁺、Tb³⁺离子共掺的3种BaCa₂(BO₃)₂荧光粉的相纯度、发光性质、浓度猝灭现象进行研究。结果表明:3种荧光粉在VUV波段有较好的吸收,基质吸收带位于140～190 nm范围。Ce³⁺在BaCa₂(BO₃)₂的最低4f5d跃迁带位置在360 nm附近,其5d→²F_J(J=5/2, 7/2)发射峰分别位于393,424 nm。Tb³⁺掺杂的样品在172 nm激发下的发射光谱由4个窄带组成,分别对应⁵D₄→⁷F_J(J=3,4,5,6)的跃迁,其中占主导位置的是⁵D₄→⁷F₅的跃迁,大约位于543 nm处,主要为绿光发射。在Ce³⁺,Tb³⁺离子共掺杂的BaCa₂(BO₃)₂光谱中,观察到Ce³⁺-Tb³⁺离子间有能量传递。     

Study of the interfacial structure and chemistry of CVD κ-Al2O3/TiC multilayer coatings

This article describes the interfacial regions in CVD grown TiC/κ-Al₂O₃ multilayers. A number of microanalytical techniques were used including HREM, EDX and EELS. Occasionally, the first 50 nm of the alumina layers deposited on the intermediate TiC layers grew as a cubic alumina, heavily faulted, containing small amounts of sulphur (S), maybe as a stabiliser. The presence of slightly rounded TiC (111) facets may act as preferred nucleation sites for the cubic Al₂O₃ phase, with a ‘cube on cube’ orientation relationship. In this way the nucleation of κ-Al₂O₃ is less favourable. After some tens of nanometres the cubic phase cannot be stabilised any longer and the layer continues to grow as κ-Al₂O₃. A number of observations point towards the reaction zone (RZ) being η- and/or γ-Al₂O₃. The diffraction work and the FFT analysis of the HREM images show that the RZ is an fcc phase with a=7.9 Å, which matches with η- and γ-Al₂O₃. The EELS Al fine structure indicate more tetrahedral Al ions than in κ-Al₂O₃, as in η- and γ-Al₂O₃. The RZ contains small amounts of S, as has been reported for γ-Al₂O₃. Due to the structural similarities between η- and γ-Al₂O₃ it was not possible to determine which of these cubic phases is present in the RZ.