Dielectric permittivities, polarization-electric-field hysteresis loops, and domain structures have been measured as a function of temperature in relaxor-based ferroelectric single crystals (PbMg 1/3 Nb 2/3 O 3 ) 0.68 (PbTiO 3 ) 0.32 ͑PMN-32%PT͒ for ͗110͘ cub and ͗211͘ cub orientations. Contrary to the pure PbMg 1/3 Nb 2/3 O 3 ͑PMN͒, PMN-32%PT exhibits apparent crystallographic orientation dependences of dielectric permittivities, polarizations, domain structures and phase transitions. With a prior field-cooled treatment, a field-induced state, perhaps of orthorhombic symmetry, is evidenced and coexists with the rhombohedral symmetry in the low-temperature region. This field-induced phase is manifested by an extra dielectric peak observed near 373 K for the ͗211͘ cub orientation. A relaxation mechanism which is responsible for the so-called diffuse phase transition crosses a wide temperature region of ϳ340-400 K and results from fluctuations between rhombohedral and tetragonal states. In order of increasing temperature ͑without a prior field-cooled treatment͒, PMN-32%PT undergoes successive phase transformations: rhombohedral phase→coexistence of rhombohedral and tetragonal phases→tetragonal phase→coexistence of tetragonal and cubic phases→cubic phase.
Three hitherto unknown eight-electron rhodium/silver alloy nanoclusters, [RhAg21{S2P(O n Pr)2}12] (1), [RhHAg20{S2P(O n Pr)2}12] (2), and [RhH2Ag19{S2P(O n Pr)2}12] (3), have been isolated and fully characterized. Cluster 1 contains a regular Rh@Ag12 icosahedral core, whereas 2 and 3 exhibit distorted RhH@Ag12 and RhH2@Ag12 icosahedral cores. The single-crystal neutron structure of 2 located the encapsulated hydride at the center of an enlarged RhAg3 tetrahedron. A similar position was found by neutron diffraction for one of the hydrides in 3, whereas the other hydride is trigonally coordinated to Rh and an elongated Ag–Ag edge. The solid-state structures of 1–3 possess C 1 symmetry due to the asymmetric arrangement of the surrounding capping Ag atoms. Our investigation shows that the insertion of one hydride dopant provokes the elimination of one capping silver atom on the cluster surface, resulting in the general formula [RhH x @Ag21–x {S2P(O n Pr)2}12] (x = 0–2), which maintains the same number of cluster electrons as well as neutral charge. Clusters 1–3 exhibit an intense emission band in the NIR region. Contrarily to their PdAg21 and PdHAg20 relatives, the 4d orbitals of the encapsulated heterometal are somewhat involved in the optical processes.
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