Structural transition in the normal state of the superconductor Mo3Sb7

Low-temperature X-ray diffraction measurements on a correlated-electron superconductor Mo₃Sb₇ revealed that the high-temperature cubic state with the Ir₃Ge₇ type structure (space group ) transforms to tetragonal below T_S=53 K, at which spin-gap formation was recently suggested. The effect of electron correlations to the structural instability is briefly discussed in connection with the condensation of the high-temperature local moments to the spin-singlet-like state.     

Structural characterization and AC conductivity of bis tetrapropylammonium hexachlorado-dicadmate, [N(C3H7)4]2Cd2Cl6

Synthesis, crystal structure, vibrational study, ¹³C, ¹¹¹Cd CP-MAS-NMR analysis and electrical properties of the compound [N(C₃H₇)₄]₂Cd₂Cl₆, are reported. The latter crystallizes in the triclinic system (space group , Z = 2) with the following unit cell dimensions: a = 9.530(1) Å, b = 11.744(1) Å, c = 17.433(1) Å, α = 79.31(1)°, β = 84.00(1)° and γ = 80.32(1)°. Besides, its structure was solved using 6445 independent reflections down to R = 0.037. The atomic arrangement can be described by alternating organic and inorganic layers parallel to the plan, made up of tetrapropylammonium groups and Cd₂Cl₆ dimers, respectively. In crystal structure, the inorganic layer, built up by Cd₂Cl₆ dimers, is connected to the organic ones through van der Waals interaction in order to build cation-anion-cation cohesion. Impedance spectroscopy study, reported in the sample, reveals that the conduction in the material is due to a hopping process. The temperature and frequency dependence of dielectric constants of the single crystal sample has been investigated to determine some related parameters to the dielectric relaxation.     

Enhanced characteristics of Ba5SmTi3Nb7O30 ferroelectric nanocrystalline ceramic prepared by mechanical activation process: A comparative study

In the present work, structural, dielectric, ferroelectric, piezoelectric and pyroelectric properties of tungsten-bronze structured Ba₅SmTi₃Nb₇O₃₀ ceramics, synthesized by mechanical activation and conventional solid-state reaction processes, have been studied with an objective of comparing the properties of the specimens synthesized by the two processes. X-ray diffraction analysis shows the formation of the compound in an orthorhombic structure by both the processes. Scanning electron microscopy reveals the formation of a fine granular microstructure in the specimen synthesized by mechanical activation process compared to the specimen synthesized by conventional solid-state method. The specimen prepared using mechanical activation process exhibits improved electrical properties with higher dielectric constant, lower dielectric loss and higher resistivity. The effective remanent polarization () value, d₃₃ value and pyroelectric coefficients are also observed to be higher in the sample synthesized by the mechanical activation process.     

The specific heat and thermal conductivity of Eccosorb CR-124 between 800 mK and 6 K

Eccosorb CR-124 is a castable iron-loaded epoxy resin with excellent absorption properties for electromagnetic waves in the GHz range. It is commonly used in low temperature instruments to absorb thermal radiation. The specific heat c(T) of Eccosorb CR-124 was measured between 800 mK and 6 K with the heat pulse method. The results were fitted to the function , with T being the temperature in Kelvin. In addition, the thermal diffusivity D(T) of Eccosorb CR-124 was determined. At a temperature of 2.3 K, a peak is observed in D(T). Consequently, the thermal conductivity λ(T) of Eccosorb CR-124 features two distinct regimes. Below 2.3 K, it fits the function . Above 2.3 K, it fits the function .     

Stability analyses of the beam tube cooling system in the KATRIN source cryostat

The Karlsruhe Tritium Neutrino Experiment (KATRIN) will measure the mass of the electron antineutrino with a sensitivity of , based on the precise measurement of the T₂β spectrum in a region close to the endpoint. This requires a T₂ source, which can provide 10¹¹β decay electrons per second. The KATRIN source cryostat consists in its centre of a 10 m long beam tube of 90 mm inner diameter, operated at 30 K. Molecular T₂ is injected in the beam tube through a central injection chamber and pumped at either tube end. The T₂ density profile must have a stability of 10^-3 in order to limit the systematic errors, yielding stringent requirements on the beam tube temperature homogeneity and stability of . This shall be achieved with a design, where the thermal radiation from the vacuum pumps is almost entirely absorbed by LN₂ and He heat exchangers on the pump ports. The beam tube itself is cooled with two-phase tubes that are part of a Ne thermosiphon. After describing the thermal environment of the beam tube, the design parameters and the operational limits of the thermosiphon will be discussed. This is followed by a detailed analysis of its dynamic behaviour, based on experimental data taken in the primary He cooling system. A “tailor-made” Ne condenser design is presented, enabling the suppression of the primary He temperature variations by two orders of magnitude, from c. to below .     

Structural and optical properties of polycrystalline CdSexTe1−x (0 ≤ x ≤ 0.4) thin films

CdSe_xTe_1−x (0 ≤ x ≤ 0.4) ternary thin films have been deposited on quartz substrates at room temperature by a single source thermal evaporation. X-ray diffraction patterns and transmission electron microscope micrographs of these films showed that the films were of polycrystalline texture over the whole range studied and exhibit predominant cubic (zinc blende) structure with strong preferential orientation of the crystallites along (1 1 1) direction. Linear variation of the lattice constant with mole fraction x is observed obeying Vegard's law. The dependence of the optical constants, the refractive index n and extinction coefficient k, of the films on the mole fraction x was studied in the spectral range of 400-2500 nm. The normal dispersion of the refractive index of the films could be described using the Wemple-DiDomenco single-oscillator model. CdSe_xTe_1−x thin films of different composition have two direct and indirect transitions corresponding to energy gaps and . The variation in either or with x indicates that this system belongs to the amalgamation type. The variation follows a subquadratic dependence and the bowing parameters were found to be 0.36 and 0.48 eV for the direct, and indirect energy gaps, respectively. Direct linear variation of the ratio N/m^* with x is observed.     

Synthesis and characterization of a new organic dihydrogenomonophosphate [3,5-(CH3O)2C6H3NH3]2(H2PO4)2

Chemical preparation, crystal structure, calorimetric studies and spectroscopic investigation are given for a new organic cation dihydrogenomonophosphate [3,5-(CH₃O)₂C₆H₃NH₃]₂(H₂PO₄)₂. This compound is triclinic with the following unit cell parameters: a=9.030(6) Å, b=16.124(5) Å, c=8.868(3) Å, α=75.04(3)°, β=110.71(4)°, γ=104.61(1)°, Z=4, V=1148.0(1) Å³, Z=2 and ρ_cal.=1.454 g cm⁻³. Crystal structure was solved and refined to R=0.04, 2752 independent reflections. The atomic arrangement can be described as inorganic layers of H₂PO₄⁻ anions parallel to planes, between which are located the organic groups. Solid-state and MAS-NMR spectroscopies are in agreement with the X-ray structure. Ab initio calculations allow the attribution of the phosphorous and carbon signals to the independent crystallographic sites and to the various atoms of the organic groups.     

Dielectric, electrical and magnetoelectric characterization of (x)Ni0.8Zn0.2Fe2O4 + (1 − x)Pb0.93La0.07(Zr0.60Ti0.40)O3 composites

The structural, electrical, dielectric, magnetic and magnetoelectric properties of (x)Ni_0.8Zn_0.2Fe₂O₄ + (1 − x)Pb_0.93La_0.07(Zr_0.60Ti_0.40)O₃ (x = 0, 0.15, 0.30, 0.45 and 1) have been studied by means of various experimental techniques. Polycrystalline samples of this series have been prepared by the double sintering ceramic method. X-ray diffraction data analysis revealed purity of the composites. Microstructural analysis using scanning electron microscopy mode depicts the presence of two phases in contact with each other. Dielectric properties were studied at and well above room temperature. Temperature dependent variation of the dielectric constant show diffused phase transition which can be well described by fitting the Lorentz-type relation, . Observation of well-saturated ferroelectric hysteresis loop and magnetic hysteresis loop for composites indicates that ferroelectric and magnetic ordering exist simultaneously at room temperature. The static value of magneto electric voltage coefficient (α_E) has been studied as a function of magnetic field at room temperature for all the composites. The maximum value of α_E is 7.53 mV/(cm Oe) for 85% PLZT-15% NZFO composites.