Phase Separation in Metal Oxides

Abstract

A fascinating phenomenon, recently found to occur in certain transition-metal oxides, is phase separation wherein pure, nominally monophasic oxides of transition metals with well-defined compositions separate into two or more phases over a specific temperature range. Such phase separation is entirely reversible, and is generally the result of a competition between charge-localization and -delocalization, the two situations being associated with contrasting electronic and magnetic properties. Coexistence of more than one phase, therefore, gives rise to electronic inhomogeneity and a diverse variety of magnetic, transport, and other properties, not normally expected of the nominal monophasic composition. An interesting feature of phase separation is that it covers a wide range of length scales anywhere between 1-200 nm. While cuprates and manganates, especially the latter, provide excellent examples of phase separation, it is possible that many other transition-metal compounds with extended structures will be found to exhibit phase separation.

Electronic phase separation and other novel phenomena and properties exhibited by mixed-valent rare-earth manganites and related materials

“…Nowhere is it manifested better than the rare-earth manganites. Thus, these materials of high chemical homogeneity consist of different spatial regions with different electronic order (Mathur & Littlewood 2003;Rao et al 2004;Dagotto 2005;Shenoy et al 2006), a phenomenon that has come to be known as 'phase separation'. These regions can be static or dynamic and can be tuned by the application of external stimuli like a magnetic field.…”

“…In addition, there is overwhelming evidence that these oxides with high chemical homogeneity can show spatially inhomogeneous structures, i.e. regions showing different electronic orders (Mathur & Littlewood 2003;Rao et al 2004;Dagotto 2005;Shenoy et al 2006). While many issues pertaining to these oxides have been understood, their science has many puzzles and challenges in addition to the promise of applications.…”

Synthesis, spectroscopic characterization, and computational studies of 2-cyano-6-hydroxybenzothiazole: a key synthetic intermediate of firefly luciferin

“…It is thus uneconomical and impractical for large-scale synthesis. The widespread classical cyanation methods to prepare aromatic nitriles are Rosenmund-von Braun 15 and Sandmeyer reactions, 16 in which aryl diazonium and aryl halides are applied as starting materials ( Figure 2). Although these methods are widely exploited, they suffer from some challenges including harsh reaction conditions, metal waste production, and low yields.…”

Electron spin resonance study of the magnetic states in the Pr0.2Sr0.8Mn1−xRuxO3 (x=0, 0.1)

“…4 Recently, it was observed that the CMR effect was considerably modified when the FMM and antiferromagnetic insulator (AFMI) ground states compete to give a magnetic phase separation state at low temperature. 5 For Mn 3+ -rich compounds, the substitution at the Mn site by a magnetic cation with a formal charge higher than 4+ showed the possibility to create FM in an AFM matrix, because not only it changes the carrier density but also introduces a change of interactions between Mn ions and the substituted cations. 6 Ru is a potential candidate to induce metallicity and ferromagnetism in these manganites due to its ability to adopt two valences Ru 4+ and Ru 5+ , which can both participate to strong super-exchange FM interactions with Mn 3+ .…”