Anomalous Conductivity in the Rutile Structure Driven by Local Disorder

Abstract

Many rutile-type materials are characterized by a softness in shear with pressure which is coupled to a Raman-active librational motion. Combining direct studies of anion positions in SnO2 with measurements of its electronic properties, we find a correlation between O sublattice disorder between 5 and 10 GPa and an anomalous decrease up to 4 orders of magnitude in electrical resistance. Hypotheses into the atomistic nature of the phenomenon are evaluated via ab initio calculations guided by extended X-ray absorption fine structure spectroscopy analysis, and the most likely mechanism is found to be the displacement of single anions resulting from the pressure-induced softening of the librational mode. On the basis of this mechanism, we propose that the same behavior should feature across all materials exhibiting a rutile → CaCl2 phase transition and that conductivity in other rutile-type materials could be facilitated at ambient pressure by appropriate design of devices to enhance defects of this nature.

Pressure-Dependent Colossal Resistivity and Anomalous Optical Signatures in FeSbO4

“…At moderate pressures (5–7 GPa) in the absence of any apparent structural changes, the resistance R P steeply rises to 650 GΩ with a huge resistance gain ∼ 4 × 10 6 compared to its ambient value R P =0 of 167 KΩ (Figure , Run-1). Experimental and theoretical investigations of FeSbO 4 have focused on its electronic properties, for example, its oxygen vacancies, , and are distinct compared to other isostructural compounds, as they are exclusively n-type materials. Upon further compression, the electrical resistance changes its slope and exhibits a plateau between 7 and 12 GPa, while its color turns to bright orange.…”

Stable and metastable structures of tin (IV) oxide at high pressure

“…librations. Under the cumulant expansion of the EXAFS equation, the difference between the long-range average interatomic lengths measured by XRD and the instantaneous lengths measured by EXAFS can be used to determine the degree of parallel and perpendicular disordering in a system [37], which we previously used to diagnose the polaron-doping mechanism of anomalous conductivity in rutile-type SnO2 at modest pressures [9].…”

“…The same transition in rutile-type SiO2 (stishovite) may have implications for understanding the seismic properties of the lower mantle [39]. When compressed in a hydrostatic medium of He, the transition is completed at 15.4 GPa [9], but can be driven at much lower pressures by non-hydrostatic stresses [2,8]. Figure 2 shows corresponding Rietveld and EXAFS analysis of SnO2 in the CaCl2 phase following compression to 25 GPa (determined by ruby photoluminescence) in a quasi-hydrostatic medium of Ne.…”

“…Similarly, we have recently observed drastic changes to electronic properties in binary oxide materials which result from perturbations of oxygen atomic positions within well-known structures. In rutile-type SnO2 [9] and GeO2 [10] slight displacement of oxygen atoms—facilitated by softening librational lattice mode inherent to the rutile structure—can cause spontaneous band gap closure which, in the case of SnO2 corresponds to an increase in electrical conductivity spanning four orders of magnitude. In well-known structures of binary oxides, pressure can thus induce anion disorder, generating polarons which contribute to the electronic band structure with such great effect as to change the bulk properties of the materials.…”