Direct Zircon-to-Scheelite Structural Transformation in YPO₄ and YPO₄:Eu³⁺ Nanoparticles Under High Pressure

Abstract

The high-pressure behavior of zircon-structured YPO 4 (with/without Eu 3+ doping) nanoparticles was examined at room temperature using in situ synchrotron X-ray diffraction (XRD) and photoluminescence (PL) measurements. In contrast with the reported XRD results of bulk YPO 4 upon compression, the nanoparticles showed a distinct transition sequence: zircon phase → scheelite phase (∼18 GPa) without the metastable monazite phase. By the return to ambient pressure, both XRD and PL results revealed that the scheelite phase could be reserved. Further Raman experiments helped us to identify the valuable mode ν 1 (A g ) of the scheelite structure in the quenched samples. The dopants effect, quasi-hydrostatic stress, and nanoscale-induced surface energy difference are considered to explain the high-pressure behavior of the nanoparticles. It is proposed that the nanoscale-induced higher surface energy contribution plays a crucial role in the distinctive high-pressure behavior of the nanoparticles.

High-Pressure Stability and Compressibility of Zircon-Type YV1–xPxO4:Eu3+ Solid-Solution Nanoparticles: An X-ray Diffraction and Raman Spectroscopy Study

“…The same can be concluded for RPO 4 compounds in which it is difficult to get a single high-pressure scheelite phase at room temperature. 25,27 Here, we analyze the compressibility by performing Rietveld refinements. Since the YV 1−x P x O 4 :Eu 3+ solid solutions are isomorphic, we adopted the atom positional parameters of zircon-type YPO 4 crystal for the YV 1−x P x O 4 :Eu 3+ (x = 0.5, 0.7, 1.0) samples.…”

Pressure-induced amorphization of YVO4:Eu3+nanoboxes

“…An interesting question still to solve is the effect of the pressure-induced amorphization and short range phase transition to a scheelite-type structure on the local structure of Eu for technological applications [4,9,10,12,13], but also to obtain local information of changes of the local crystalline structure by the analysis of its emission spectrum [35,36]. This is due to its electronic energy levels scheme which consists of seven 7 F J (J = 0-6) multiplets spaced almost uniformly and five 5 D J (J = 0-4) multiplets well separated in energy [37].…”

“…In fact, several works performed on zircon-type (space group I4 1 /amd) compounds have shown that, in general, the high-pressure behavior of the nanomaterial cannot be extrapolated from the behavior of the bulk. For instance, bulk zircon-type YPO 4 transforms to a scheelitetype structure (space group I4 1 /a) passing through a monazite-type structure (space group P 2 1 /n) while nanocrystals of this compound directly transforms from zircon to scheelite [2][3][4], in YCrO 4 the opposite occurs [5]. In addition, an interesting effect can be found in the propensity of nanomaterials to undergo the so called pressure-induced amorphization (PIA) [4,6].…”

“…For instance, bulk zircon-type YPO 4 transforms to a scheelitetype structure (space group I4 1 /a) passing through a monazite-type structure (space group P 2 1 /n) while nanocrystals of this compound directly transforms from zircon to scheelite [2][3][4], in YCrO 4 the opposite occurs [5]. In addition, an interesting effect can be found in the propensity of nanomaterials to undergo the so called pressure-induced amorphization (PIA) [4,6]. The density of surface defects can increase abruptly in the surrounding of a phase transition eventually giving rise to its frustration [1].…”

“…It has been proposed as a refractive index sensor [11], and also as a red nanophosphor in nanosize probes for drug delivery systems [4,12,13]. Under high pressure bulk YVO 4 undergoes a structural phase transition to a scheelite-type structure at 7.5 GPa [14][15][16] as most zircon compounds.…”