Geometric and electronic structure of lanthanide orthophosphate nanoparticles determined with X-rays

Abstract

The evolution of the geometric and electronic structures within the entire series of lanthanide orthophosphate nanoparticles ͑ϳ2-ϳ 5 nm͒ has been determined experimentally with X-ray diffraction and near edge X-ray absorption fine structure spectroscopy. In particular, the interplay between electronic structure, crystal morphology, and crystal phase has been systematically studied. A missing local order in the crystal structure accompanied by multiple ion sites in the nanoparticles was revealed to be due to the small crystal size and large surface contribution. All lanthanide ions were found to be in "3+" configuration and accommodated in three different crystallization states: the larger lanthanide ions ͑La, Ce, Pr, Nd, Sm͒ in the monoclinic phase, the smaller ones ͑Er, Tm, Yb, Lu͒ in the tetragonal phase, and the intermediate lanthanide ions ͑Eu, Gd, Tb, Dy, Ho͒ in a "mixed phase" between monoclinic and tetragonal phases.

Size-dependent magnetic ordering and spin dynamics in DyPO4and GdPO4nanoparticles

“…This indicates the tetragonal DyPO 4 lattice to be "softer" than the monoclinic sister compounds, in agreement with the larger size of its unit cell. 11 For the nanoparticles, we observe quite similar phonon contributions above 10 K for both Dy and Gd. The phonon contributions are, thus, much higher than for the bulk materials, which can be attributed principally to the extra vibrational contributions coming from the TEHP ligand molecules, as is further discussed below.…”

“…For the DyPO 4 nanoparticles, this number is found to be as high as ≈20%. Since the mean particle core diameter is 2.6 nm, 11 implying ≈150 Dy 3+ spins per particle, one-third of which will be in the inner core and, thus, fully AF coordinated, this fraction would then correspond to ≈30 uncompensated spins and ≈70 compensated spins in the surface layer of the DyPO 4 particle cores. For the GdPO 4 nanoparticles, on the other hand, we find μ ≈ 80μ B , corresponding to about 11 uncompensated Gd 3+ (S = 7 2…”

High-resolution nonresonant x-ray Raman scattering study on rare earth phosphate nanoparticles

“…The nanoparticles were synthesized by colloidal chemistry, and their surface was passivated by amine chains. The crystallinity, morphology, and size of the particles were investigated using x-ray diffraction and transmission electron microscopy and have been previously reported [26]. In this work, we report x-ray Raman spectra of the The beam from three consecutive undulators was monochromated using a combination of a Si(111) doublecrystal and a Si(333) channel-cut monochromator.…”

“…First of all, the O shell, being a relatively low-lying semicore shell, interacts strongly with the valence electrons such that the spectrum is broadened into a band with an ∼0.5-eV bandwidth. In contrast with the very localized character of the f 4 orbitals, the d 5 orbitals have a larger radial extent (see figure 5) and are strongly mixed with oxygen p 2 and phosphor p 3 orbitals [26]. In addition, the presence of a multitude of different surface states with differing energies causes an additional broadening of the valence spectral structures.…”

“…It would be interesting to study the semicore excitation spectra in this class of systems (e.g., bulk versus nanoparticles) more closely using XRS [34,35]. For instance, oxygen K-edge XAS spectra of the entire lanthanide series have revealed particle-size effects on the oxygen-lanthanide covalent bonding [26].…”