F. Ritter

Determination of the primary solidification area of the icosahedral phase in the ternary phase diagram of Zn-Mg-Y

We present the results of our research on the ternary phase diagram of the Zn-Mg-Y system. We focus on the liquidus surface which is relevant for the preparation of the icosahedral phase. Two sections of the phase diagram and the primary crystallization area of the icosahedral phase have been determined.

Phononic filter effect of rattling phonons in the thermoelectric clathrate Ba8Ge40+xNi6-x.

One of the key requirements for good thermoelectric materials is a low lattice thermal conductivity. Here we present a combined neutron scattering and theoretical investigation of the lattice dynamics in the type I clathrate system Ba-Ge-Ni, which fulfills this requirement. We observe a strong hybridization between phonons of the Ba guest atoms and acoustic phonons of the Ge-Ni host structure over a wide region of the Brillouin zone, which is in contrast with the frequently adopted picture of isolated Ba atoms in Ge-Ni host cages. It occurs without a strong decrease of the acoustic phonon lifetime, which contradicts the usual assumption of strong anharmonic phonon-phonon scattering processes. Within the framework of ab initio density-functional theory calculations we interpret these hybridizations as a series of anticrossings which act as a low-pass filter, preventing the propagation of acoustic phonons. To highlight the effect of such a phononic low-pass filter on the thermal transport, we compute the contribution of acoustic phonons to the thermal conductivity of Ba8Ge40Ni6 and compare it to those of pure Ge and a Ge-46 empty-cage model system.

Temperature dependence of Bi2O3 structural parameters close to the α–δ phase transition

This article presents the results of in situ X-ray powder diffraction, Raman spectroscopy, and electrical impedance spectroscopy of the α-phase of Bi2O3, at 0.1 MPa in the temperature range below and above the α–δ-phase transition. This work demonstrated subtle nonlinear temperature variations of the cell parameters, of the hard-mode Raman shift, and of the activation energy of electrical conductivity in the temperature range about 100–120°C below the α–δ phase transition temperature T Tr ≈ 725°C in Bi2O3. At T < 600°C, the linear variation of the inverse dielectric susceptibility (χ −1) correlates well with the hard mode frequency shift Δ(ω 2) of Raman A1g mode as Δ(χ −1)/Δ(ω 2) ≈ 5.5 × 10−7 cm2. A structural model describing the mechanism of O2− anion distribution and electric dipole disordering in the vicinity of T Tr is discussed.

Elements of the Phase Diagram of YbInCu4

To clearify how the valence transition temperature of YbInCu 4 is connected with the composition of the grown crystals, we investigated the phase diagram. Since elements of the liquidus curve of the system Yb-In-Cu were already known we focused on the solidus curve in the surrounding of the valence changing YbInCu 4 . Bridgman-technique for crystal growth was used. The composition of the solidified crystals was determined by means of wavelength-dispersive X-ray analysis. The valence transition temperature is measured via the lattice constant by low temperature X-ray diffraction. Results are, that the assumed exchange of Yb and In, which is indicated in the formula Yb x In 2-x Cu 4 seems to be not correct. Not the quasi-binary section for constant copper content should be used, but one for constant ytterbium content. Starting compositions with an excess of ytterbium lead to the substitution of indium by copper. The valence transition temperature of these crystals is shifted from 40K to 70K.

Unusual weak magnetic exchange in two different structure types: YbPt2Sn and YbPt2In

We present the structural, magnetic, thermodynamic and transport properties of the two new compounds YbPt(2)Sn and YbPt(2)In. X-ray powder diffraction shows that they crystallize in different structure types, the hexagonal ZrPt(2)Al and the cubic Heusler type, respectively. Despite quite different lattice types, both compounds present very similar magnetic properties: a stable trivalent Yb(3+), no evidence for a sizeable Kondo interaction and very weak exchange interactions with a strength below 1 K as deduced from specific heat C(T). Broad anomalies in C(T) suggest short range magnetic ordering at about 250 mK and 180 mK for YbPt(2)Sn and YbPt(2)In, respectively. The weak exchange and the low ordering temperature result in a large magnetocaloric effect as deduced from the magnetic field dependence of C(T), making these compounds interesting candidates for magnetic cooling. In addition we found in YbPt(2)In evidences for a charge density wave transition at about 290 K. The occurrence of such transitions within several RET2X compound series (RE = rare earth, T = noble metal, X = In, Sn) is analyzed.

Spin correlations and Dzyaloshinskii-Moriya interaction in Cs2CuCl4

We report on electron spin resonance (ESR) studies of the spin relaxation in Cs

Thermoanalytical Investigations to Understand the Dependence Between the Growth Method and Crystal Properties of Valence Changing “YbInCu4”

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BEHAVIOR OF BI1.7PB0.3SR2CA2CU3OX AT HIGH TEMPERATURE

CuCl

Low-temperature structural investigations of the frustrated quantum antiferromagnets

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{\mathrm{Cs}}_{2}\mathrm{Cu}\left({\mathrm{Cl}}_{4-x}{\mathrm{Br}}_{x}\right)

. The main source of the ESR linewidth at temperatures