Heribert Wiedemeier

Bio: Heribert Wiedemeier is an academic researcher from Rensselaer Polytechnic Institute. The author has contributed to research in topics: Crystal growth & Phase diagram. The author has an hindex of 19, co-authored 102 publications receiving 1494 citations.

Refinement of the structures of GeS, GeSe, SnS and SnSe

Abstract: The orthorhombic structures (Pbnm-Di~; No. 62) of GeS, GeSe, SnS and SnSe have been refined (X-ray diffractometer data: 319 hkl, R = 0.029; 370 hkl, R = 0.061 ; 386 hkl, R = 0.062; 506 hkl, R = 0.076). The bond distances are: Ge S = 2.438(1), 2.448(2) A; Ge-Se = 2.574(2),2.564(3) A; Sn-S = 2.665(2),2.627(4) A; SnSe = 2.793(2), 2.744(3) A. The structures of these compounds reveal systematic variations of bond lengths, bond angles and of nonbonding distances. These properties as well as their temperature dependence compared to those of related compounds allow to treat these structures as different configurations of a hypothetical reaction path of a phase transition GeS type ---+ TII type ---+ NaCl type.

The Thermal Expansion of GeS and GeTe

Abstract: The thermal expansion of GeS has been studied above room temperature up to the melting point of 658 ± 5°C by X-ray diffraction techniques using a 190 mm diameter Unicam high temperature camera. The thermal expansion of the crystallographic axes is linear with distinct changes in the rate of expansion at about 250°C, 370°C and 510°C. No first-order structural transformation was observed for this system up to the melting point. The results of additional studies on GeTe are in general agreement with those of others and confirm trends in the thermal expansion behavior of the germanium monochalcogenide series. Die thermische Ausdehnung des GeS und GeTe Die thermische Ausdehnung des GeS wurde rontgenographisch mittels einer 190 mm Unicam Hochtemperaturkamera von Zimmertemperatur bis zum Schmelzpunkt von 658 ± 5°C untersucht. Die thermische Ausdehnung der kristallographischen Achsen ist linear mit betonten Anderungen der Ausdehnungskoeffizienten bei ungefahr 250°C, 350°C und 510°C. Eine Strukturumwandlung erster Ordnung wurde fur diese. Verbindung bis zum Schmelzpunkt nicht beobachtet. Die Ergebnisse zusatzlicher Messungen am GeTe stimmen mit denen anderer uberein und bestatigen den Trend im thermischen Ausdehnungsverhalten der Germaniummonochalkogenide.

Cadmium zinc telluride and its use as a nuclear radiation detector material

Abstract: We present a comprehensive review of the material properties of cadmium zinc telluride (CZT, Cd1ˇxZnxTe) with zinc content xa 0:1‐0.2. Particular emphasis is placed on those aspects of this material related to room temperature nuclear detectors. A review of the structural properties, charge transport, and contacting issues and how these are related to detector and spectrometer performance is presented. A comprehensive literature survey and bibliography are also included. # 2001 Elsevier Science B.V. All rights reserved.

Giant piezoelectricity of monolayer group IV monochalcogenides: SnSe, SnS, GeSe, and GeS

Abstract: We predict enormous, anisotropic piezoelectric effects in intrinsic monolayer group IV monochalcogenides (MX, M=Sn or Ge, X=Se or S), including SnSe, SnS, GeSe, and GeS. Using first-principle simulations based on the modern theory of polarization, we find that their piezoelectric coefficients are about one to two orders of magnitude larger than those of other 2D materials, such as MoS2 and GaSe, and bulk quartz and AlN which are widely used in industry. This enhancement is a result of the unique “puckered” C2v symmetry and electronic structure of monolayer group IV monochalcogenides. Given the achieved experimental advances in the fabrication of monolayers, their flexible character, and ability to withstand enormous strain, these 2D structures with giant piezoelectric effects may be promising for a broad range of applications such as nano-sized sensors, piezotronics, and energy harvesting in portable electronic devices.

Enhanced sodium-ion battery performance by structural phase transition from two-dimensional hexagonal-SnS2 to orthorhombic-SnS.

Abstract: Structural phase transitions can be used to alter the properties of a material without adding any additional elements and are therefore of significant technological value. It was found that the hexagonal-SnS2 phase can be transformed into the orthorhombic-SnS phase after an annealing step in an argon atmosphere, and the thus transformed SnS shows enhanced sodium-ion storage performance over that of the SnS2, which is attributed to its structural advantages. Here, we provide the first report on a SnS@graphene architecture for application as a sodium-ion battery anode, which is built from two-dimensional SnS and graphene nanosheets as complementary building blocks. The as-prepared SnS@graphene hybrid nanostructured composite delivers an excellent specific capacity of 940 mAh g–1and impressive rate capability of 492 and 308 mAh g–1 after 250 cycles at the current densities of 810 and 7290 mA g–1, respectively. The performance was found to be much better than those of most reported anode materials for Na-ion ...

Orbitally driven giant phonon anharmonicity in SnSe

Abstract: Understanding elementary excitations and their couplings in condensed matter systems is critical for developing better energy-conversion devices. In thermoelectric materials, the heat-to-electricity conversion efficiency is directly improved by suppressing the propagation of phonon quasiparticles responsible for macroscopic thermal transport. The current record material for thermoelectric conversion efficiency, SnSe, has an ultralow thermal conductivity, but the mechanism behind the strong phonon scattering remains largely unknown. From inelastic neutron scattering measurements and first-principles simulations, we mapped the four-dimensional phonon dispersion surfaces of SnSe, and found the origin of the ionic-potential anharmonicity responsible for the unique properties of SnSe. We show that the giant phonon scattering arises from an unstable electronic structure, with orbital interactions leading to a ferroelectric-like lattice instability. The present results provide a microscopic picture connecting electronic structure and phonon anharmonicity in SnSe, and offers new insights on how electron–phonon and phonon–phonon interactions may lead to the realization of ultralow thermal conductivity. Tin selenide is at present the best thermoelectric conversion material. Neutron scattering results and ab initio simulations show that the large phonon scattering is due to the development of a lattice instability driven by orbital interactions.