The magnetic susceptibility of TMTSF-DMTCNQ under pressure

The susceptibility of TMTSF-DMTCNQ was measured in the newly discovered highly-conducting state under pressure. At a pressure of 12 kbar, the susceptibility χ_m (with the core diamagnetism subtracted) changes sign from the room-temperature paramagnetic value and becomes diamagnetic at a temperature of approximately 30 K. At a temperature of 5–10 K χ_m reaches a value of approximately ?7 × 10^?4 emu mole^?1. This value is about 3 times larger than the previously reported diamagnetism of HMTSF-TCNQ.     

Adsorption of nitrogen on platinum

The adsorption and desorption of nitrogen on a platinum filament have been studied by thermal desorption techniques. Nitrogen adsorption becomes significant only after any carbon contamination is removed from the surface by heating the platinum filament in oxygen, and after the CO content in the background gas is reduced substantially. At room temperature nitrogen populates an atomic tightly bound β-state, E^≠ = 19 kcal mole^?1. The saturation coverage of the (3-state is 4.5 × 10¹⁴ atoms cm^?2. Formation of the (β-state is a zero order process in the pressure range studied. At 90 K two additional α₁- and α₂-desorption peaks are observed. The activation energy for desorption for the α₂-state is 7.4 kcal mole^?1 at low coverage decreasing to 3 kcal mole^?1 at saturation of this state, 6 × 10 molecules cm^?2. The maximum total coverage in the α-states was 1.2 × 10¹⁵ molecules cm^?2. A replacement process between the β- and α-states has been observed where each atom in the (β-state excludes two molecules from the α-state.     

Diffusion and compressibility of sodium on the (110) plane of tungsten

The surface diffusion parameters and the compressibility of sodium on the (110) plane of tungsten have been measured using the field emission fluctuation method for sodium coverages from 0.2 to 3 × 10¹⁴ atoms cm^?2 and for temperatures from 170 to 500 K. Two temperature regimes can be defined. In the high temperature regime (? 300 K) the diffusion is essentially normal with an activation energy ranging from 0.28 to 0.58 eV and a preexponential coefficient D₀ from 10^?8.1 to 10^?2.7 cm² s^?1. In this regime the compressibility increases with temperature indicating an effective repulsive adatoms interaction. In the low temperature regime (? 300 K) the diffusion coefficient decreases with temperature at high coverage and slowly increases with temperature at lower coverage. The transition between both regimes appears on the compressibility versus temperature curve as an inflection point. The comparison of the present results with slow electron diffraction results furnishes strong evidence that the observed transition corresponds to a continuous short-range order-disorder transition.     

High temperature heat capacity of the LaSn3 and CeSn3 compounds

The high temperature heat capacities of LaSn₃ compound and CeSn₃ intermediate valence compound have been obtained from enthalpic contents measurements, using the technique of drop calorimetry in the 400–1200 K temperature range.The heat capacity behaviour of CeSn₃ has been compared with that of LaSn₃ and the quantitative difference between the two trends is explained in terms of residual promotional energy of the 4? electron of Ce to the conduction band.     

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.     

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.     

Thermal expansion of CuGaSe2

The thermal expansion coefficients of CuGaSe₂ are measured in the temperature range from 300 to 670 K by an X-ray technique and are found to be α_a = 13.1 × 10^?6K^?1 and α_c = 5.2 × 10^?6K^?1 for the lattice parameters a and c, respectively. Some general trends in the temperature dependence of the tetragonal distortion of the I-III-VI₂ and II-IV-V₂ compounds are considered.     

Effect of pressure on the properties of DH diode lasers in AlxGa1-xAsySb1-y/GaSb system

Abstract

A helium pressure appparatus for diode laser studies up to 1.4 GPa at 77–300 K has been developed. DH lasers with Al_xGa_1-xAs_ySb_1-y active layers (x=0-0.05) lattice-matched to GaSb substrates have been investigated. It has been shown that in lasers with x,y=0 pressure dependences of the threshold current density (J_th) and the average electron lifetime at the threshold (τ) measured at 80 K depend strongly on the quadratic recombination of L^c ₆ electrons, the characteristic coefficient being 1.5×10^?11 cm³s^?1. The pressure-composition equivalence coefficient dx/dP=2.2×10^?10 Pa^?1 has been obtained for the lowest temperatures used.     

Thermodynamic and magnetic properties of LaSn3

Thermal expansion coefficient between 77 and 900K, isothermal compressibility in the 0–80 Kbar pressure range, magnetic susceptibility between 77 and 1300 K and heat capacity at constant pressure in the 20–300 K temperature range were determined for the LaSn₃ compound. From the experimental data, the specific heat at constant volume was calculated and the thermal dependence of the Debye's parameter θ_D was obtained. The electron contribution to the heat capacity was also determined from the high temperature data. The magnetic properties confirm that there is no evidence of the existence of a magnetic moment localized on La atoms, in contrast with a previous report and in agreement with the general assumptions. A little anomaly found in the expansion coefficient, in the isothermal compressibility and in the specific heat is discussed in terms of a lattice order-disorder phenomenon.     

Superficial migration of tritium physisorbed on monocrystalline nickel (111)

The aim of this study is the measurement of superficial migration coefficient of tritium physisorbed on monocrystalline nickel without chemisorbed sublayer. The chosen crystalline orientation was (111) because it offers the greatest concentration of adsorption sites per square centimeter. A clean surface sample is obtained by mechanical polishing, chemical etching and finally ionic bombardment by high purity argon gas. The pressure in the experimental vessel is maintained below 10^?9 torr, by liquid helium cryopumping after zeolite sorption pumping.A little spot of adsorbed tritium is produced by introduction of a finite amount of tritium gas on the clean surface of the nickel sample through a stainless steel tube. Temperatures of nickel and of the gas introduction tube are respectively regulated at 5 K and 35 K. Tritium is used as a radioactive marker and its 10 keV β-radiation is measured by a channeltron type detector which permits the localization of the deposit without acting on the surface. We observed that tritium sorbed at 5 K is quite immobile (at the time scale of our experiment). After heating up to a fixed temperature T chosen between 10 K and 20 K, the deposite profile variation in function of time is observed to determine the superficial diffusion coefficient D. For the values of T from 13 K to 20 K, D varies from 10×10^?6 to 150×10^?6 cm² sec^?1. A diffusion activation energy of 200 cal mole^?1 is deduced from the exponential increase of the curve. A vibrational frequency can be evaluated to 3×10¹² sec^?1. The rate of desorption permits the evaluation of sorption energy at about 1800 cal mole^?1 in good agreement with usual results concerning physorption of H₂ on metals.     

Finite temperature lattice softening in CeSn3

Results of temperature dependent Mossbauer effect measurements on Sn in CeSn₃ and LaSn₃ are presented. An anomalous increase in the Sn mean squared displacement (MSD) in CeSn₃ in the 50K region surrounding 135K has been observed. A phenomological model is developed which relates the results to previous measurements on CeSn₃. This model discusses lattice softening effects near continuous, isomorphic phase transitions such as occur in a number of rare earth compounds.     

Diffusion of titanium in slightly reduced rutile

The self-diffusion of ⁴⁴Ti in slightly reduced rutile. TiO_2?δ, was measured along the c axis over the temperature range of 1000–1100°C between 0.2 and 1 × 10^?18atm. oxygen pressure. These measurements enabled the determination of the defect structure of TiO_2-δ for 0.02 ?gd ? 0.001. For oxygen pressures between 1 × 10^?13 and 1 × 10^?16atm. at 1058.4°C random tetravalent titanium atoms are the predominant defects evident from self-diffusion. The enthalpy of motion was determined as ΔH_m = 57.03 ± 4.9% kcal/mole. From the activation energy at 1.69 × 10^?16atm., the enthalpy of formation for tetravalent titanium interstitials was determined as ΔH_f = 276 ± 15.6% kcal/mole.For oxygen pressures less than 1 × 10^?16atm. at 1058.4°C, the tracer diffusion coefficient shows a continuous decline as the oxygen pressure is lowered. Comparisons with thermogravimetric studies and consideration of the similarity in structure between nonstoichiometric point defect phases and the first homologous series phase indicate that the order-disorder transition retains a considerable degree of short range order below the critical concentration in the form of Wadsley defects.     

Sound velocity in single crystals of synthetic opals

The [111] longitudinal sound velocity (v _L) in a single-crystal synthetic opal has been measured at a frequency of 10 MHz in the temperature range 4.2–300 K. At 300 K, v _L=2.1×10⁵ cm/s. The quantity dv _L/v _{300 K}(T) (where v _T,K?v_{300 K}) in the ranges 4.2–200 and 200–300 K behaves in the way typical of amorphous and crystalline solids, respectively.     

Heat capacity and thermodynamic properties of α-Fe2O3 in the region 300–1050 K. antiferromagnetic transition

The heat capacity of synthetic α-Fe₂O₃ has been measured in the range 300–1050K by adiabatic shield calorimetry with intermittent energy inputs and temperature equilibration in between. A λ-type transition, related to the change from antiferro- to paramagnetism in the compound, is delineated and a maximum heat capacity of about 195 JK^?1 mole^?1 is observed over a 3 K interval around 955 K. Values of thermodynamic functions have been derived and C_P (1000K), [H⁰(1000K)-H⁰(0)], and [S⁰(1000K)-S⁰(0)] are 149.0JK^?1 mole^?1, 115.72 kJ mole^?1, and 252.27 JK^?1 mole^?1, respectively, after inclusion of earlier low-temperature results [X⁰ (298.15K)-X⁰(0)]. The non-magnetic heat capacity is estimated and the thermodynamic properties of the magnetic transition evaluated. The results are compared with spin-wave calculations in the random phase approximation below the Néel temperature and the Oguchi pair model above. An upper estimate of the total magnetic entropy gives 32.4JK^?1 mole^?1, which compares favorably with that calculated for randomization of five unpaired electron spins on each iron, ΔS = 2R ln 6 = 29.79 JK^?1 mole^?1 for α-Fe₂O₃. The critical exponent α in the equation $\text{C}{}_{\mathrm{m}}\text{= (}\text{A}\text{α}\text{) [(|T}{}_{\mathrm{<mtext>n</mtext>}}\text{?T|/T}{}_{\mathrm{<mtext>n</mtext>}}\text{)?1]}{}^{\mathrm{?\alpha }}\text{+ B}$ is ?(0.50±0.10) below the maximum and 0.15±0.10 above, for T_n = 955.0K. The high temperature tail is discussed in terms of short range order.     

Absorption of Dy3+ and Nd3+ ions in BaR 2F8 single crystals

The Dy³⁺ absorption and excitation spectra of BaY₂F₈ and BaYb₂F₈ single crystals are investigated in the ultraviolet, vacuum ultraviolet, and visible ranges at a temperature of 300 K. These crystals exhibit intense broad absorption bands due to the spin-allowed 4f-5d transitions in the range (56–78) × 10^?3 cm^?1 and less intense absorption bands that correspond to the spin-forbidden transitions in the range (50–56) × 10^?3 cm^?1. The Nd³⁺ absorption spectra of BaY₂F₈ single crystals are studied in the range (34–82) × 10^?3 cm^?1 at 300 K for different crystal orientations.     

The adsorption and desorption of oxygen on the Pt(110) surface; A thermal desorption and LEED/AES study

The interaction of oxygen with a Pt(110) crystal surface has been investigated by thermal desorption mass spectroscopy, LEED and AES. Adsorption at room temperature produces a β-state which desorbs at ~800 K. Complete isotopic mixing occurs in desorption from this state and it populates with a sticking probability which varies as (1 ? θ)², both observations consistent with dissociative adsorption. The desorption is second order at low coverage but becomes first order at high coverage. The saturationcoverage is 3.5 × 10¹⁴ mol cm^?2. The spectra have been computer analysed to determine the fraction desorbing by first (β₁) and second (β₂) order kinetics as a function of total fractional coverage θ using this fraction as the only adjustable parameter. The β₁ desorption commences at θ ～ 0.25 and β₁ and β₂ contribute equally to the desorption at saturation. The kinetic parameters for β₁ desorption were calculated from the variation of peak temperature with heating rate as ν₁ = 1.7 × 10⁹ s^?1 and E^≠₁ = 32 kcal mole^?1 whereas two different methods of analysis gave consistent parameters ν₂ = 6.5 × 10^?7 cm² mol^?1 s^?1 and E^≠₂ = 29 and 30 kcal mole^?1 for β₂ desorption. The kinetics of desorptior are discussed in terms of the statistics for occupation of near neighbour sites. While many fea tures of the results are consistent with this picture, it is concluded that simple models considering either completely mobile or immobile adlayers with either strong or zero adatom repulsion are not completely satisfactory. The thermal desorption surface coverage has been correlated with the AES measurements and it has been possible to use the AES data for PtO as an internal standard for calibration of the AES oxygen coverage determination. At low temperature (170 K) oxygen populates an additional molecular α-state. Adsorption into the α- and β-states is competitive for the same sites and pre-saturation of the β-state at 300 K excludes the α-state. This, together with the AES observation that the adsorption is enhanced and faster at 450 than 325 K suggests a low activation energy for adsorption into the β-state.     

Equation of state and thermal expansivity of LiF and NaF

The high-pressure and high-temperature behaviors of LiF and NaF have been studied up to 37 GPa and 1000 K. No phase transformations have been observed for LiF up to the maximum pressure reached. The B1 to B2 transition of NaF at room temperature was observed at ～28 GPa, this transition pressure decreases with temperature. Unit-cell volumes of LiF and NaF B1 phase measured at various pressures and temperatures were fitted using a P–V–T Birch–Murnaghan equation of state. For LiF, the determined parameters are: α₀ = 1.05 (3)×10^?4 K^?1, dK/dT = ?0.025 (2) GPa/K, V ₀ = 65.7 (1) Å³, K ₀ = 73 (2) GPa, and K′ = 3.9 (2). For NaF, α₀ = 1.34 (4)×10^?4 K^?1, dK/dT = ?0.020 (1) GPa/K, V ₀ = 100.2 (2) Å³, K ₀ = 46 (1) GPa, and K′ = 4.5 (1).     

Volume properties and compressibility of the graphite-potassium-mercury compounds

Abstract

The volume properties of graphite intercalation compounds (GIGS) C4KHg and of the initial intermetallic compounds KHg and KHg₂ have been investigated in the piston-cylinder apparatus, using the direct volumetric technique, under pressures up to 25 kbar. The compounds, average compressibility K₊, was determined to be 3.8×10^?3 kbar^?1 for C₄KHg, 3.0×10^?3 kbar-^?1 for C₈KHg, 4.8×10^?1 kbar^?1 for KHg, and 4.0 ×10^?1 kbar^?1 for KHg₂ at pressures of 0-20 kbar. The compressibility of the “two-dimensional” KHg layer in the GIC under various pressure conditions has been estimated. These estimates permit comparison of KHg properties in the “three dimensional” and “quasi-two dimensional” states. It was concluded that the influence of the graphite matrix on the intercalant is insignificant for this type ternary GIC.     

DX-Like behavior of Se-impurity centers in gasb under hydrostatic pressure

Abstract

Hall coefficient (R_H) and electrical resistivity measurements have been performed as a function of temperature (between 77 K and 300 K) and under hydrostatic pressures (up to 15 kbar) on a set of Se-doped GaSb samples with impurity concentrations in the range 8×10¹⁷ cm^?3 - 1×10¹⁸ cm^?3. With increasing pressure at 300 K, the electrons are strongly trapped into a resonant impurity level. The pressure induced occupation of this level leads to time-dependent effects at T<120 K. The activated thermal electron emission over a potential barrier E<sb>B = 300×30 meV gives clear evidence for a large lattice relaxation around the impurity centers characteristic for DX-like behavior.