The unusual property of negative thermal expansion is of fundamental interest and may be used to fabricate composites with zero or other controlled thermal expansion values. Here we report that colossal negative thermal expansion (defined as linear expansion <−10−4 K−1 over a temperature range ~100 K) is accessible in perovskite oxides showing charge-transfer transitions. BiNiO3 shows a 2.6% volume reduction under pressure due to a Bi/Ni charge transfer that is shifted to ambient pressure through lanthanum substitution for Bi. Changing proportions of coexisting low- and high-temperature phases leads to smooth volume shrinkage on heating. The crystallographic linear expansion coefficient for Bi0.95La0.05NiO3 is −137×10−6 K−1 and a value of −82×10−6 K−1 is observed between 320 and 380 K from a dilatometric measurement on a ceramic pellet. Colossal negative thermal expansion materials operating at ambient conditions may also be accessible through metal-insulator transitions driven by other phenomena such as ferroelectric orders.

Strong correlation between spins and conduction electrons is key in spintronic materials and devices. A few ferro-or ferrimagnetic transition metal oxides such as La 1 À x Sr x MnO 3 , Fe 3 O 4 , CrO 2 and Sr 2 FeMoO 6 have spin-polarized conduction electrons at room temperature, but it is difficult to find other spin-polarized oxides with high Curie temperatures (well above room temperature) and large magnetizations for spintronics applications. Here we show that an A-and B-site-ordered quadruple perovskite oxide, CaCu 3 Fe 2 Re 2 O 12 , has spin-polarized conduction electrons and is ferrimagnetic up to 560 K. The couplings between the three magnetic cations lead to the high Curie temperature, a large saturation magnetization of 8.7 m B and a half-metallic electronic structure, in which only minority-spin bands cross the Fermi level, producing highly spin-polarized conduction electrons. Spin polarization is confirmed by an observed low-field magnetoresistance effect in a polycrystalline sample. Optimization of CaCu 3 Fe 2 Re 2 O 12 and related quadruple perovskite phases is expected to produce a new family of useful spintronic materials.

Thermophilic rhodopsin (TR) is a light-driven proton pump from the extreme thermophile Thermus thermophilus JL-18. Previous studies on TR solubilized with detergent showed that the protein exhibits high thermal stability and forms a trimer at room temperature but irreversibly dissociates into monomers when incubated at physiological temperature (75 °C). In the present study, we used resonance Raman (RR) spectroscopy, solid-state NMR spectroscopy, and high-speed atomic force microscopy to analyze the oligomeric structure of TR in a lipid environment. The obtained spectra and microscopic images demonstrate that TR adopts a pentameric form in a lipid environment and that this assembly is stable at the physiological temperature, in contrast to the behavior of the protein in the solubilized state. These results indicate that the thermal stability of the oligomeric assembly of TR is higher in a lipid environment than in detergent micelles. The observed RR spectra also showed that the retinal chromophore is strongly hydrogen bonded to an internal water molecule via a protonated Schiff base, which is characteristic of proton-pumping rhodopsins. The obtained data strongly suggest that TR functions in the pentameric form at physiological temperature in the extreme thermophile T. thermophilus JL-18. We utilized the high thermal stability of the monomeric form of solubilized TR and here report the first RR spectra of the monomeric form of a microbial rhodopsin. The observed RR spectra revealed that the monomerization of TR alters the chromophore structure: there are changes in the bond alternation of the polyene chain and in the hydrogen-bond strength of the protonated Schiff base. The present study revealed the high thermal stability of oligomeric assemblies of TR in the lipid environment and suggested the importance of using TR embedded in lipid membrane for elucidation of its functional mechanism.