Local lattice distortions and thermal transport in perovskite manganites

Measurements of thermal conductivity versus temperature and magnetic field are reported for perovskite manganites that exhibit ferromagnetic (FM), charge-ordering (CO), antiferromagnetic, and/or structural phase transitions. The data reveal a dominant lattice contribution to the heat conductivity with {kappa}{approximately}1{minus}2 W/mK near room temperature. The rather low values, implying a phonon mean free path on the order of a lattice spacing, are shown to correlate with static local distortions of the MnO{sub 6} octahedra. Modifications of the local structure are responsible for abrupt anomalies in the zero-field {kappa} at the FM, CO, and structural transitions, and for colossal magnetothermal resistance near the FM transition. {copyright} {ital 1997} {ital The American Physical Society

STUDY OF Y-Ba-Cu-O SUPERCONDUCTORS PREPARED WITH THE OXALATE PRECIPITATION/EVAPORATION METHOD

A study is presented on a series of Y-Ba-Cu-O superconductors prepared with the Oxalate Precipitation/Evaporation method. The effect of the preparation conditions on the properties of these superconductors has been studied with X-rays, scanning electron microscopy, Raman spectroscopy, and magnetic measurements. The experiments show that good quality superconductors can be fabricated with this preparation procedure and also indicate that the properties of these materials are very sensitive to the preparation conditions