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We report by the first time a high pressure X-ray diffraction and Raman spectroscopy study of cobalt ferrite (CoFe2O4) nanoparticles carried out at room temperature up to 17 GPa. In contrast with previous studies of nanoparticles, which proposed the transition pressure to be reduced from 20-27 GPa to 7.5-12.5 GPa (depending on particle size), we found that cobalt ferrite nanoparticles remain in the spinel structure up to the highest pressure covered by our experiments. In addition, we report the pressure dependence of the unit-cell parameter and Raman modes of the studied sample. We found that under quasi-hydrostatic conditions, the bulk modulus of the nanoparticles (B0=204 GPa) is considerably larger than the value previously reported for bulk CoFe2O4 (B0=172 GPa). In addition, when the pressure medium becomes non-hydrostatic and deviatoric stresses affect the experiments, there is a noticeable decrease of the compressibility of the studied sample (B0=284 GPa). After decompression, the cobalt ferrite lattice parameter does not revert to its initial value, evidencing a unit cell contraction after pressure was removed. Finally, Raman spectroscopy provides information on the pressure dependence of all Raman-active modes and evidences that cation inversion is enhanced by pressure under non-hydrostatic conditions, being this effect not fully reversible. [ABSTRACT FROM AUTHOR]

We have successfully synthesized for the first time a Ti-doped ZrSiO4 powder (stoichiometry Zr0.95Ti0.05SiO4) via a sol-gel route. The structural and vibrational properties have been characterized by X-ray diffraction, electron microscopy and Raman spectroscopy. Zr0.95Ti0.05SiO4 has a tetragonal zircon-type structure with a = 6.5981(2) Å and c = 5.9810(2) Å. Eight of its Raman-active modes have been measured and assigned. We also performed high-pressure synchrotron X-ray diffraction experiments. The structural behavior was studied up to 31 GPa. At this pressure, we found evidence of the onset of a phase transition, coexisting the low-pressure polymorphs (zircon) with the typical high-pressure polymorph of ZrSiO4 (reidite-type). From the analysis of unit-cell volume versus pressure using a Birch-Murnaghan equation of state, in the quasi-hydrostatic pressure regime (P < 10.5 GPa), we have determined a bulk modulus of 297 GPa. This magnitude represents an enhancement of a 30% in the value of this parameter if compared with un-doped zircon-type ZrSiO4 (bulk modulus < 227 GPa). The low compressibility of Zr0.95Ti0.05SiO4 converts this compound in a very good candidate for many technological applications. The effect of pressure on the linear compressibility of the lattice parameters is also analyzed. [ABSTRACT FROM AUTHOR]

We have performed high-pressure synchrotron X-ray diffraction experiments on nanoparticles of pure tin dioxide (particle size ∼30 nm) and 10 mol % Fe-doped tin dioxide (particle size ∼18 nm). The structural behavior of undoped tin dioxide nanoparticles has been studied up to 32 GPa, while the Fe-doped tin dioxide nanoparticles have been studied only up to 19 GPa. We have found that both samples present at ∼13 GPa a second-order structural phase transition from the ambient pressure tetragonal rutile-type structure ( P4 2 /mnm ) to an orthorhombic CaCl 2 -type structure (space group Pnnm ). No phase coexistence was observed for this transition. Additionally, pure SnO 2 presents a phase transition to a cubic structure at ∼24 GPa. The evolution of the lattice parameters with pressure and the room-temperature equations of state are reported for the different phases. The reported results suggest that the partial substitution of Sn by Fe induces an enhancement of the bulk modulus of SnO 2 . Results are compared with previous studies on bulk and nanocrystalline SnO 2 . The effects of pressure on Sn-O bonds are also analyzed. [ABSTRACT FROM AUTHOR]