Crystal structure and dielectric properties of LaYbO3 ceramics

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, r, 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 r 26, Q × fr20 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