Thermal expansion op NbSe2 and TaS2

The lattice parameters a₀ and c₀ of the hexagonal 2H polytype of NbSe₂; have been measured over the temperature range 156–478 K for a₀, and 138–482 K for c₀. The lattice parameter c₀ of the hexagonal 2H polytype of TaS₂ has been measured between 151 and 472 K. The lattice parameters a₀ and c₀ for the octahedral 1T polytype of TaS₂ been measured between 165 and 488 K. Over these temperature ranges, the following average coefficients of thermal expansion have been measured; 2H-NbSe₂, 6.6 × 10^?6K^?1 along the a-axis, 19.9 × 10^?6 K^?1 along the c-axis; 2H-TaS₂, 15.6 × 10^?6 K^?1 along the c-axis; IT-TaS₂, 12.7 × 10^?6 K^?1 along the c-axis. The parameter c₀ of 1T-TaS₂ undergoes two transitions which may be explained in terms of charge density waves.     

Electrophysical parameters of <Emphasis Type="Italic">c</Emphasis>-oriented Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> films with a low concentration of antistructural defects

Epitaxial c-oriented Bi₂Te₃ films 1.2 μm in thickness are grown by the hot wall method for a low supersaturation of the vapor phase over the surface of mica substrates. The hexagonal unit cell parameters a = 4.386 Å and c = 30.452 Å of the grown films almost coincide with the corresponding parameters of stoichiometric bulk Bi₂Te₃ crystals. At T = 100 K, the Hall concentration of electrons in the films is on the order of 8 × 10¹⁸ cm^?3, while the highest values of the thermoelectric coefficient (α ≈ 280 μV K^?1) are observed at temperatures on the order of 260 K. Under impurity conduction conditions, conductivity σ of the films increases upon cooling in inverse proportion to the squared temperature. In the temperature range 100–200 K, thermoelectric power parameter α²σ of Bi₂Te₃ films has values of 80–90 μW cm^?1 K^?2.     

Thermodynamic properties of the CeSn3 mixed valence compound

We have measured on the CeSn₃ compound, the expansion coefficient between 80 and 800 K at normal pressure, the isothermal compressibility in the 0–8 GPa pressure range at room temperature and the heat capacity at constant pressure in the 60–300 K temperature range. The experimental data were compared with those previously found for the isomorphous LaSn₃ phase, assumed as a proper reference material for the study of the intermediate valency states in CeSn₃. Both the thermal expansion (3α) and the isothermal compressibility (k) of CeSn₃ show behaviours quite different from those of LaSn₃: for instance, in the standard conditions, 3α is 55 × 10^?6K^?1for CeSn₃ and 38 × 10^?6K^?1for LaSn₃; k is 15 × 10^?12 Pa^?1 and 12 × 10^?12 Pa^?1 respectively for CeSn₃ and LaSn₃. The thermal behaviour of the molar specific heat at constant pressure of CeSn₃ is similar to that of LaSn₃ for temperatures lower than 50 K. In the 70–300 K temperature range, the heat capacity of CeSn₃ is clearly higher than that of LaSn₃, ΔC_p being maximum near 150 K. The analysis of the calorimetric data show that the electronic coefficient γ of CeSn₃ is temperature dependent: its value varies from 53 mJ K^?2 mole^?1 at low temperature 24 mJ K^?2 mole^?1 at 300 K.     

A high-resolution study of the 14.4-μm infrared band of deuterofluoroform

The FT-IR spectrum of the ν₃ parallel band of deuterofluoroform has been recorded at a resolution of 0.0045 cm^?1. Nine independent spectral parameters were determined which reproduce some 650 observed wavenumbers with a standard error of 3 × 10^?4 cm^?1. The constants derived for the ν₃ band are (in cm^?1): ν₀ = 694.2822(3); B₀ = 0.3309321(9); B₃ = 0.3302464(11); α^B = 6.859(10) × 10^?4; α^C = 1.429 × 10^?4; D₃^J = 3.168(3) × 10^?7; D₀^J = 3.188(3) × 10^?7; D_JK³ = 4.766 × 10^?7; D_JK⁰ = 4.864 × 10^?7; and D_K⁰ ? D_K³ = 2 × 10^?10.     

Rate coefficient and transition probability of XeO

Rate coefficients of XeO(¹S) at various vibrational levels (v = 0, 1 and 2) were observed by measuring absolute intensities of the spectrum in the low-pressure d.c. glow of an Xe-O₂ mixture discharge. The association coefficients at the various levels are K_a0 = 2.4×10^-34 cm⁶ at v = 0, K_a1 = 1.1 × 10^-34 cm⁶ atv = 1, and K_a2 = 9.1 × 10^-35 cm⁶ at v = 2. The transition probability from XeO(¹S)₀ to $\text{XeO(}{}^1\text{D)u}$ is estimated to be A₀ = 1.3 × 10⁵ sec^-1.     

Magnetization behaviour of DyAl2 single crystals

We report the theoretical interpretation of the magnetization and the magnetocrystalline anisotropy of ferromagnetic DyAl₂ single crystals between 4.2 and 60 K and magnetic fields up to 15 T. Good agreement between theory and experiment is obtained by using three temperature independent parameters: the two crystal field parameters B₄ = (?0.50 ± 0.05) × 10^?4 meV, B₆ = ? (0.51 ± 0.05) × 10^?6 meV and the Curie temperature T_c = (62 ± 2) K.     

Effect of hydrostatic pressure on the magnetocrystalline anisotropy constant K1 of iron and nickel

Previous values of the pressure dependence of the magnetocrystalline anisotropy constant K₁ of iron and nickel were revised. These values of K₁^?1 ($\text{dK}{}_1\text{dp}$) depend on the magnetic field for iron, and do not for nickel. The value in iron extrapolated to infinitely strong magnetic field is ?7.8×10^?6 bar^?1 at room temperature and ?7.3×10^?6 bar^?1 at 77K, and in nickel at 15 KOe is ?7.5×10^?6 bar^?1 at room temperature and ?2.8×10^?6 bar^?1 at 77K.     

Infrared study of superlattice formation in Ti1+xSe2

Infrared reflectivity measurements have been made on two Ti_1+xSe₂ crystals of different stoichiometry over the range 200 cm^?1 to 4000 cm^?1 before and after the formation of a 2a_o × 2c_o superlattice. In both crystals at room temperature a heavily damped Drude edge is observed at about 1000 cm^?1. At liquid helium temperatures, below the phase transition, the Drude minimum of a non-stoichiometric crystal ($\text{x ? 0.02, T}{}_{\mathrm{c}}\text{= 155 K}$) is at 750 cm^?1 whereas the low temperature minimum of a more stoichiometric sample (T_c = 198 K) is below 350 cm^?1. Also, new absorption peaks are seen to develop below T_c at about 3700 cm^?1 and 3300 cm^?1 for the non- stoichiometric and stoichiometric-crystals respectively. The observed phenomena are related to the energy gaps which open up in the band structure below the phase transition temperature.     

P–V–T equation of state of rhodium oxyhydroxide

A high pressure X-ray diffraction study of RhOOH was carried out up to 17.44?GPa to investigate the compression behavior of an oxyhydroxide with an InOOH-related structure. A fit to the third-order Birch–Murnaghan equation of state gave K₀?=?208?±?6?GPa, and K′?=?9.4?±?1.3. The temperature derivative of the bulk modulus was found to be ?K/?T?=??0.06?±?0.02?GPa K^?1. The refined parameters for volume thermal expansion were α₀?=?2.7?±?0.3?×?10^?5 K^?1; α₁?=?1.7?±?1.1?×?10^?8 K^?2 in the polynomial form (α(T)?=?α_0?+?α₁(T?300)). Our results show that RhOOH is very incompressible, and has a higher bulk modulus than other InOOH-structured oxyhydroxides (e.g. δ-AlOOH, ε-FeOOH, and γ-MnOOH).     

Observation of the radiative transition ψ → γE(1420)

We have observed a radiative transition from the ψ to a state decaying into K_SK^±π^?, with mass M = 1.44_?0.015^+0.01 GeV/c² and width Γ = 0.05_?0.02^+0.03 GeV/c². We tentatively identify this state as the E(1420). Assuming that this state is an isospin singlet, we have determined the branching fraction product $\text{B(ψ → γ}\text{E}\text{) × B(}\text{E}\text{×}\text{K}\text{K}\text{π) = (3.6 ± 1.4) × 10}{}^{\mathrm{?3}}$.     

Electron paramagnetic resonance in deuterated nickel fluosilicate

Electron paramagnetic resonance measurements in single crystals of NiSiF₆. 6D₂O were made at K, Ku and Ka bands at 4.2 K and between 77 K and 300 K. The measured g values were in the range 2.23–2.26, while the zero-field splitting parameter D varied from ?(0.185 ± 0.005) cm^?1 at 4.2 K to ?(0.53 ± 0.01) cm^?1 at 298 K. The parameters of the trimolecular hexagonal unit cell were determined to be approximately a = 9.28 Å, c = 9.58 Å from powder X-ray diffraction measurements at room temperature.     

Transport properties of n-type ferromagnetic semiconductor HgCr2−xInxSe4(x = 0.100)

Measurements of the electrical conductivity, magnetoresistance, and Hall effect were performed on a n-type ferromagnetic semiconductor HgCr_2?xIn_xSe₄(x = 0.100) single crystal from 6.3 to 296 K in magnetic fields up to 1.19×l0⁶A/m. The conductivity decreases rapidly near the Curie temperatureT_c (≈120 K) as the temperature is raised. A large peak in the magnetoresistance is observed near T_c. The Hall effect measurements indicate that the temperature dependence of the conductivity and the magnetoresistance are due mostly to a change in electron mobility. The electron mobility is 1.2 × 10^?2 m²/V · s at 6.3 K, and decreases rapidly near T_c with the rise in temperature. Then it increases slowly from 5.5 × 10^?4 m²/V · s at 160 K to 7.5 × 10^?4 m²/V · s at 241 K. This temperature dependence of the electron mobility can be explained in terms of the spin-disorder scattering which takes into account the exchange interaction between charge carriers and localized magnetic moments.     

In-situ X-ray diffraction study on β-CrOOH at high pressure and high-temperature

ABSTRACT

High pressure hydrous phases with distorted rutile-type structure have attracted much interest as potential water reservoirs in the Earth’s mantle. An in-situ X-ray diffraction study of β-CrOOH was performed at high pressures of up to 6.2?GPa and high-temperatures of up to 700?K in order to clarify the temperature effect on compression behaviors of β-CrOOH. The P-V-T data fitted to a Birch–Murnaghan equation of state yielded the following results: isothermal bulk modulus K_T0?=?191(4)?GPa, temperature derivative (?K_T/?T)_P?=??0.04(2)?GPa?K^?1, and volumetric thermal expansion coefficient α?=?3.3(2)?×?10^?5?K^?1. In this study, at 300?K, the a-axis became less compressible at pressures above 1–2?GPa. We found that the pressure where the slopes of a/b and a/c ratios turned positive increased with temperature. This is the first experimental study indicating the temperature dependence of the change in the axial compressibility in distorted rutile-type M³⁺OOH.     

Analysis of the 2ν3 band of 12CD3F at 5.06 μm recorded under high resolution

The 2ν₃(A₁) band of ¹²CD₃F near 5.06 μm has been recorded with a resolution of 20–24 × 10^?3 cm^?1. The value of the parameter (α^B ? α^A) for this band was found to be very small and, therefore, the K structure of the R(J) and P(J) manifolds was unresolved for J < 15 and only partially resolved for larger J values. The band was analyzed using standard techniques and values for the following constants determined: ν₀ = 1977.178(3) cm^?1, B″ = 0.68216(9) cm^?1, D″_J = 1.10(30) × 10^?6 cm^?1, α^B = (B″ ? B′) = 3.086(7) × 10^?3 cm^?1, and β^J = (D″_J ? D′_J) = ?3.24(11) × 10^?7 cm^?1. A value of α^A = (A″ ? A′) = 2.90(5) × 10^?3 cm^?1 has been obtained through band contour simulations of the R(J) and P(J) multiplets.     

Ferroelastic phase transition and anomalous elastic and thermal properties of betaine borate (CH3)3NCH2COO·H3BO3

The temperature and pressure derivatives of the elastic constants of orthorhombic betaine borate, (CH₃)₃NCH₂COO·H₃BO₃, have been determined by measuring temperature and stress induced shifts of resonance frequencies of thick plates at ca. 15 MHz in the range between 140 and 300 K and 0 and 3 kbar. The elastic ‘shear’ resistance c₄₄ exhibits a value as low as 0.0492×10¹⁰Nm^-2at 293 K. With decreasing temperature c₄₄ approaches zero at ca. 142.5 K, indicating an acoustic soft mode behaviour connected with a ferroelastic phase transition. The softening of c₄₄ is described in a good approximation by c₄₄(T)_p=0 =alogT/T₀ with a=0.0663×10¹⁰Nm^-2 and T₀ = 139.5 K. Further, c₄₄ decreases with increasing pressure according to the linear relation c₄₄(p)_{T=293 K} = 0.0492?0.184×10^-4p (p in bar, c₄₄ in 10¹⁰ Nm^-2). All other elastic constants show a quite normal temperature and pressure dependence. At 293 K the transition is induced by a pressure of 2.65 kbar. The transition temperature T_c depends linearly on pressure according to T_c = 142.5+0.0568 p (pinbar, T_cinK). Passing through the transition no discontinuous change of the lattice constants is observed. The three principal coefficients of thermal expansion and the pressure derivatives of the dielectric constants exhibit discontinuities at the transition. The transition is of strongly second order.     

High-resolution vibration-rotation spectroscopy of fluoroform-d

The vibration-rotation spectrum of the ν₂ and ν₅ fundamentals of CDF₃ have been recorded using a Nicolet 7199 Fourier transform infrared spectrometer; in addition the Q branch and several subbands of each of these transitions have been investigated using a tunable semiconductor diode laser spectrometer. The Q branch and the K structure in several P(J) and R(J) subbands of ν₂, and in several Q branches of ν₅, are resolved and assigned for the first time. Constants derived for these bands are (in cm^?1) ν₂ = 1111.1823₆, B₂ = 0.32928₂, A₂ = 0.18872₂, α₂^B = 16.44₅ × 10^?4, α₂^B ? α₂^A = 12.43₅ × 10^?4, D₀^j = 3.7₃ × 10^?7, D₂^J = 4.8₃ × 10^?7; ν₅ = 975.39₁, B₅ = 0.33062, A₅ = 0.18887, α₅^B = 2.83₁ × 10^?4, α₅^A = 2.4₃ × 10^?4, ζ₅ = 0.736, D₅^J ? D₀^J = 1.2₂ × 10^?8. Some of these constants are nearly 100 times more precise than those reported in previous work.     

Specific features of anion transfer in HoF<Subscript>3</Subscript> crystals at high temperatures

The anionic conductivity of HoF₃ single crystals with a β-YF₃ structure (orthorhombic crystal system, space group Pnma) is investigated over a wide range of temperatures (323–1073 K). The unit cell parameters of HoF₃ crystals are as follows: a=0.6384±0.0009 nm, b=0.6844±0.0009 nm, and c=0.4356±0.0005 nm. It is revealed that the conductivity anisotropy of the HoF₃ crystals is insignificant over the entire temperature range covered. The crossover from one mechanism of ion transfer to another mechanism is observed near the critical temperature T_c≈620 K. The activation enthalpy of electrical conduction is found to be ΔH₁=0.744 eV at T<T_c and ΔH₂=0.43 eV at T>T_c. The fluorine vacancies are the most probable charge carriers in HoF₃ crystals. The fluorine ionic conductivities at temperatures of 323, 500, and 1073 K are equal to 5×10^?10, 5×10^?6, and 2×10^?3 S cm^?1, respectively.     

Raman studies of lattice dynamics in 1T-TiSe2

Raman scattering measurements were carried out on 1T-TiSe₂ above and below the phase transition temperature. Below _c many new lines appear, which are the Γ-point phonon modes folded from the original zone boundary points L, M and A due to the formation of the 2a₀ × 2a₀ × 2c₀ superlattice. Among them the strong A_1g line at 119 cm^?1 and the E_g line at 78 cm^?1 at 11 K show softening, as the temperature approaches to T_c, but the modes become overdamped before the energies go to zero.     

X-ray structure refinement and ionic conductivity of Na6.69Ca3.355(SO4)6Cl0.77F0.63

The structure of Na_6.69Ca_3.355(SO₄)₆Cl_0.77F_0.63, isostructural with fluorapatite, was determined by X-ray powder diffraction methods. The results of Rietveld refinement revealed a space group P6₃/m with lattice parameters of a?=?9.477 (2) Å, c?=?6.865 (5) Å. Final refinement led to R _F?=?1.83 % and R _B?=?7.64 %. The location of Na⁺ ions in the M (2) sites surrounding the channels was related particularly to the high polarizability of the Ca²⁺. The ionic conductivity over a wide range of temperature was investigated according to the complex impedance method. The highest overall conductivity values were found at σ _500 °C?=?1.03?×?10^?5?S?cm^?1 and E_a?=?0.70 eV.     

Tunable laser study of the ν10 + ν11 band of cyclopropane

Diode laser measurements of the ν₁₀ + ν₁₁ (l_tot = ±2) perpendicular band of cyclopropane have led to the assignments of roughly 600 lines in the 1880–1920-cm^?1 region. Most of the spectra were recorded and stored in digital form using a rapid-scan mode of operating the laser. These spectra were calibrated, with the aid of a computer, by reference to the R lines of the ν₁ + ν₂ band of N₂O. The ground state constants we obtained are (in cm^?1) B = 0.670240 ± 2.4 × 10^?5, D_J = (1.090 ± 0.054) × 10^?6, D_JK = (?1.29 ± 0.19) × 10^?6, D_K = (0.2 ± 1.1) × 10^?6. The excited state levels are perturbed at large J values, presumably by Coriolis couplings between the active E′(l_tot = ±2) and the inactive A′(l_tot = 0) states. Effective values for the excited state constants were obtained by considering only the J < 15 levels. The A₁-A₂ splittings in the K′ = 1 excited states were observed to vary as q_effJ(J + 1), with q_eff = (2.17 ± 0.17) × 10^?4 cm^?1.