Crystal structure and dielectric properties of LaYbO₃

The crystal structure and dielectric properties of LaYbO3 ceramics prepared by the mixed-oxide route have been investigated. Rietveld refinements performed on X-ray and neutron diffraction data show the room-temperature structure to be best described by the orthorhombic Pnma space group [a=6.02628(9) Å, b=8.39857(11) Å, and c=5.82717(7) Å; Z=4, and theoretical density, Dx=8.1 g/cm3] in agreement with electron diffraction experiments. LaYbO3 ceramics fired at 1600°C for 4 h attain ∼97% of Dx and their microstructures consist of randomly distributed equiaxed grains with an average size of ∼8 μm. Conventional transmission electron microscopy shows densification to occur in the absence of a liquid phase and reveals domain-free grains. The relative permittivity, εr, of LaYbO3 ceramics at radio frequencies is ∼26 in the range ∼10-300 K; however, a small dielectric anomaly is detected at ∼15 K. At room temperature and microwave frequencies, LaYbO3 ceramics exhibit εr ∼26, Q × fr∼20 613 GHz (at 7 GHz), and τf∼-22 ppm/K. Q × fr show complex subambient behavior, decreasing from a plateau value of ∼20 000 GHz between ∼300 and 200 K to a second plateau value of ∼6000 GHz at ∼90 K before decreasing to <1000 GHz at ∼10 K. The large decrease in Q × fr at low temperature may be related to the onset of antiferromagnetism at ∼2.7 K.1