Pressure-Induced Sublattice Disordering in SnO2 : Invasive Selective Percolation

Abstract

SnO_{2} powders and single crystal have been studied under high pressure using Raman spectroscopy and ab initio simulations. The pressure-induced changes are shown to drastically depend on the form of the samples. The single crystal exhibits phase transitions as reported in the literature, whereas powder samples show a disordering of the oxygen sublattice in the first steps of compression. This behavior is proposed to be related to the defect density, an interpretation supported by ab initio simulations. The link between the defect density and an amorphouslike Raman signal is discussed in terms of the invasive percolation of the anionic sublattice. The resistance of the cationic sublattice to the disorder propagation is discussed in terms of cation close packing. This result on SnO_{2} may be extended to other systems and questions a "traditional" crystallographic description based on polyhedra packing, as a decoupling between both sublattices is observed.

Extreme structural stability of Ti0.5Sn0.5O2 nanoparticles: synergistic effect in the cationic sublattice

“…Under pressure, the defect density increases until percolation and amorphization of the anionic network occur. 32 This effect has recently been confirmed by a combination of XRD and EXAFS. 47…”

“…Likewise, it was recently shown that bulk SnO 2 also exhibits such a decoupling of cationic and anionic sublattices under pressure. 32 The oxygen sublattice in bulk SnO 2 indeed transforms to a disordered array while the cationic sub-lattice shows no transformation. Such behavior is similar to what is observed in nanoparticles.…”

“…Indeed, while no phase transition has been reported using X-ray diffraction which mainly probes the cationic sub-lattice, a pressure-induced disordering has been observed in SnO 2 nanoparticles and SnO 2 bulk in using Raman spectroscopy. 12,32 This characterization technique is more sensitive to the anionic sub-lattice. Indeed, a pressure-induced disordering of the oxygen sublattice starting above 7 GPa in 3 nm particles was evidenced, with the propagation of the disorder from the shell to the core.…”

“…This effect can be discussed as resulting from the effect of defects on the decoupled anionic and cationic sublattices. 32 Thus, the interesting observation of the similarity between the Ti 0.5 Sn 0.5 O 2 and TiO 2 Raman spectra indicates that decoupling between sublattices is not observed in the solid solution (as it is in the case of SnO 2 nanoparticles) despite the presence of defects.…”

“…In SnO 2 , the B 2g mode is visible but not the B 1g one, as supported by calculations. 32 For all these vibrational modes, the oxygen atoms vibrate while cations are at rest. As already discussed for TiO 2 nanorods, the large band at ∼120 cm −1 is not expected according to the Raman selection rules but is originated by defects.…”