Phonon-based partition of (ZnSe-like) semiconductor mixed crystals on approach to their pressure-induced structural transition

The generic 1-bond → 2-mode “percolation-type” Raman signal inherent to the short bond of common A1−xBxC semiconductor mixed crystals with zincblende (cubic) structure is exploited as a sensitive “mesoscope” to explore how various ZnSe-based systems engage their pressure-induced structural transition (to rock-salt) at the sub-macroscopic scale—with a focus on Zn1−xCdxSe. The Raman doublet, that distinguishes between the AC- and BC-like environments of the short bond, is reactive to pressure: either it closes (Zn1−xBexSe, ZnSe1−xSx) or it opens (Zn1−xCdxSe), depending on the hardening rates of the two environments under pressure. A partition of II–VI and III–V mixed crystals is accordingly outlined. Of special interest is the “closure” case, in which the system resonantly stabilizes ante transition at its “exceptional point” corresponding to a virtual decoupling, by overdamping, of the two oscillators forming the Raman doublet. At this limit, the chain-connected bonds of the short species (taken as the minor one) freeze along the chain into a rigid backbone. This reveals a capacity behind alloying to reduce the thermal conductivity as well as the thermalization rate of photo-generated electrons.

Crystal structure of the Anderson-type heteropolyoxometalate; K2[H7CrIIIMo6O24]·8H2O: a redetermination revealing the position of the extra H atom in the polyanion

The title compound contains a symmetric hydrogen bond in which the H atom does not lie on a crystallographic centre of symmetry. The structure of K2[H7CrIIIMo6O24]·8H2O, namely dipotassium heptahydrogen hexamolybdochromate(III) octahydrate, previously reported by Lee [Acta Cryst. (2007), E63, i5–i7], has been redetermined in order to locate the position of the seventh H atom in the anion. Six of the H atoms are bonded to the six μ3-O atoms and form hydrogen bonds of medium strength either to water molecules or to the terminal O atoms of other polyanions. The seventh H atom forms a very short hydrogen bond between two μ2-O atoms on adjacent polyanions. This short bond, together with two normal hydrogen bonds, link the two crystallographically distinct centrosymmetric polyanions into chains along [011], while the length of this bond [2.461 (3) Å] suggests that the H atom lies at its centre, but unusually for such a bond, this point is not a crystallographic centre of symmetry.

Structure Determination of New Phases K1.65V1.78W0.22O2(AsO4)2and K2V2O2(AsO4)2

Two new phases K1.65V1.78W0.22O2(AsO4)2 and K2V2O2(AsO4)2 [1,2] belonging to KTiOPO4 family (KTP) [3] have been synthesized and characterized by single crystal X-ray diffraction. The structure of K1.65V1.78W0.22O2(AsO4)2 shows an irregular MO6 octahedra (M=78%V+22%W) with two abnormal short bonds M–O (1.774 (7) Å) and (1.824 (8) Å) which suggest that the non linear optical property could be more important. In order to show the influence of the tungsten and vanadium on the distortion of the MO6 octahedra, we substituted the tungsten by the vanadium element. The single-crystal K2V2O2(AsO4)2 consists of common VO6 octahedra with one short bond V–O (1.652(2) Å) . We used SUPERFLIP and JANA 2006 programs [4, 5] to resolve and refine these structures. The refinement by JANA 2006 led to the reliability factors: (R =0.048, Rw = 0.064) for K1.65V1.78W0.22O2(AsO4)2, and (R =0.028, Rw = 0.034) for K2V2O2(AsO4). Structure of K1.65V1.78W0.22O2(AsO4)2 Structure of K2V2O2(AsO4)2 Space group: Pc21n Space group: Pc21n Cell parameters: Cell parameters: a = 6.5322 (7) Å a = 6.5368 (2) Å b = 10.7228 (9) Å b = 10.7228 (5) Å c = 13.0782 (5) Å c = 13.0666 (4) Å

Optimized cavities for microwave applications using the new low loss LTCC material Du Pont 9k7

This paper presents two different novel methods to manufacture optimized cavity structures, which are suitable for multilayer System-in-Package (SiP) and Multi-Chip-Module (MCM) applications, in the new low temperature cofired ceramic (LTCC) material Du Pont 9k7. In contrast to standard manufacturing, the improved DP 9k7 cavities show almost perfectly orthogonal cross sections and straight edges, achieved by applying special cavity inlays or cast silicone. Ball-wedge bond wires and wedge-wedge ribbons are implemented directly to the cavity rim successfully. Therefore, these cavities are suitable for very short bond wires in complex RF systems and the introduced techniques are very promising for future applications using DP 9k7.