Vibrational properties of LaPO4 nanoparticles in mid- and far-infrared domain

Nanopowders of LaPO₄ have been grown by sedimentation-micellar method. As-prepared LaPO₄ nanoparticles with the average grain size of about 8 nm have a single-phase hydrated hexagonal structure. After thermal annealing at 600 and 800 °C, the average size of nanoparticles increases up to ∼35 and ∼50 nm, respectively, and the structure transforms into single-phase monoclinic. IR spectra of LaPO₄ nanoparticles of different size were investigated in the wide range of wavenumbers from 130 to 5000 cm^-1 in the 20-300 K temperature region. Differences between IR spectra of the bulk material and nanoparticles as well as the temperature behavior of the vibrational properties are discussed.