Cu(Cu0.44Cr4.56)Ge2O12: a close‐packed oxide with CuO4 tetra­hedra

The structure of copper(I,II) penta­chromium(III) germanate, Cu(Cu_0.44Cr_4.56)Ge₂O₁₂, contains one Cu position (m2m), one Ge position (m) and three Cr positions (2/m, m and 2). The close‐packed structure is described in terms of slabs of edge‐sharing Cr³⁺O₆ octa­hedra and isolated CuO₄ and GeO₄ tetra­hedra. These slabs are aligned parallel to the bc plane and are separated from each other by GeO₄ tetra­hedra along a. The tetra­hedral coordination observed for the Cu⁺/Cu²⁺ ions represents an unusual feature of the structure. The Cr—O and Cu—O bond lengths are compared with literature data.     

The modified Kaw's model based on rectangular voltage pulses for the calculation of the charge pumping current in mis transistors

The charge pumping current results from recombination associated with the SiO₂-Si interface traps under the gate of a MISFET when a voltage pulse is applied to the gate. The modified Kaw's model is proposed which predicts this current as a function of frequency, amplitude and average voltage of pulses with peak-to-peak amplitudes larger than the difference between the flatband and inversion voltages and with pulse transitions fast enough so that negligible capture or emission occurs during the transition. The presented modification of Kaw's model of the charge pumping effect enables to compute the dependences of the charge pumping current for various types of MIS transistors with different dimensions manufactured by different technologies.     

Structural phase transition in the 2D spin dimer compound SrCu 2 ( BO 3 ) 2

A displacive, 2nd order structural phase transition at T _s = 395 K from space group I 2 m below T _s to I 4/m c m above T _s has been discovered in the two-dimensional spin dimer compound SrCu₂(BO₃)₂. The temperature evolution of the structure in both phases has been studied by X-ray diffraction and Raman scattering, supplemented by differential scanning calorimetry and SQUID magnetometry. The implications of this transition and of the observed phonon anomalies in Raman scattering for spin-phonon and interlayer coupling in this quantum spin system will be discussed. Received 24 July 2000 and Received in final form 2 November 2000