STUDY OF THE RUTHENIUM(V) PEROVSKITES M2LNRUO6 (M=CA, LN=Y, LA, OR EU - M=SR, LN=Y - M=BA, LN=LA OR EU) BY RU-99 MOSSBAUER-SPECTROSCOPY AND OTHER TECHNIQUES

Ruthenium-99 Mössbauer spectroscopy has been used in conjunction with other techniques to examine the new perovskite phases Ca2LnRuO6 (Ln = Y, La, or Eu) and the recently reported analogous strontium and barium compounds M2LnRuO6 (M = Sr, Ln = Y; M = Ba, Ln = La or Eu). At 4.2°K the spectra show widely split magnetic hyperfine patterns (B = 56-60 T) having chemical isomer shifts in the range 0.13-0.18 mm sec-1 relative to ruthenium metal, thereby confirming the presence of magnetically ordered ruthenium(V)ions in these phases. The computed linewidths for the yttrium compounds are close to the natural value, indicative of unique ruthenium environments and the existence of crystallographic order between RuV and YIII ions on the B-sites. This is further corroborated by the observation of superlattice reflections in the X-ray powder diffraction pattern of Ca2YRuO6. Superlattice reflections are also observed for Ca2LaRuO6, Ba2LaRuO6, and Ba2EuRuO6. The Mössbauer spectra for the barium compounds feature sharp paramagnetic components in addition to the magnetically split ruthenium(V) resonances, and possible explanations for these unusual results are discussed. Magnetic susceptibility measurements above 80°K show that all the compounds follow a Curie-Weiss law with negative paramagnetic Curie temperatures, indicative of antiferromagnetism. Measurements down to 4.2°K for the calcium compounds reveal Néel temperatures in the region of 15°K when Ln = Y or La, whereas Ca2EuRuO6 appears to be ferrimagnetic. Electrical resistivity measurements on compacted powders indicate that the materials are not metallic conductors. Mössbauer and powder X-ray diffraction measurements for the phase reported as Sr2LaRuO6 indicate that it is in fact a mixture of Sr2RuO4 and a solid-solution phase of the type Sr2LaxRu1-xO4. © 1979.