Thermal-expansion-derived lattice instability in La2CuO4

We present results for the thermal expansion, (T), of both polycrystalline and single crystalline La₂CuO₄. Our results demonstrate the existence of an anomaly in (T) aroundT=35 K which is clearly intrinsic and most likely due to a lattice instability.     

Reconstruction of individual cumulative radon exposures by low-level in vivo measurements and biokinetic modeling

In vivo skull measurements of ²¹⁰Pb have been performed to assess the individual, chronic exposures of two persons living for 28 years in a house with a distinctly enhanced radon concentration of more than 10,000 Bq/m³. A partial body counter consisting of 4 HPGe detectors, which were placed close to parietal positions of the head, was used in the study. The lower limit of detection of ²¹⁰Pb activity in the skeleton was found to be 40 Bq. Lead-210 activities of up to 152 Bq were found in the test persons, whereas no activity could be measured in an unexposed control person. The cumulative uptake of ²¹⁰Pb into the body was assessed for each single test person by using the ICRP respiratory tract and the biokinetic models. A fairly good agreement (within a factor of 2) between in vivo measurements and model was achieved for these two test persons. The technique used in the study may be a useful tool to evaluate assumptions, which have to be made for the reconstruction of individual, cumulative exposures to high radon concentrations.     

Crystallographic study of tetragonal,superconducting YBa2(Cu0.93Fe0.05)3O7

Single crystal- and powder X-ray diffraction, powder neutron diffraction at room temperature and 3 K, high resolution electron microscopy and electron diffraction were used to study the crystal- and defect-structure of YBa₂(Cu_0.93Fe_0.05)₃O₇. Crystals of this compound are superconducting (T _c 80 K) and appeart to be tetragonal down to at least 3 K. The structure resembles that of the undoped YBa₂Cu₃O₇ phase with the oxygen content being very close to 7.0 and the Fe atoms preferentially occupying the Cu(1) site. A copper deficiency is shown to be present on this site too, leading to the approximate formula YBa₂(Cu_0.97Fe_0.03)₂(Cu_0.86Fe_0.10.04)O₇. High resolution electron microscopy reveals the existence of orthorhombic micro-domains, 20–30 Å in diameter, probably due to short range ordering of oxygen atoms on the O(1) site. In view of these results the structure has to be regarded as being tetragonal only in a statistical sense.     

Structural studies by electron microscopy: High-resolution observations on β-ZrO2·12Nb2O5

Reliable idealized structures for the β and γ forms of ZrO₂·12Nb₂O₅ have been deduced following the observation of lattice images, recorded at a resolution of about 0.3 nm, from crystals oriented with their short b axes parallel to the incident electron beam. The structure of the β form is confirmed by preliminary results from single crystal X-ray studies. The present observations are compared with previous work on these phases.