Because the functions of polar materials are governed primarily by their polarization response to external stimuli, the majority of studies have focused on controlling polar lattice distortions. In some perovskite oxides, polar distortions coexist with nonpolar tilts and rotations of oxygen octahedra. The interplay between nonpolar and polar instabilities appears to play a crucial role, raising the question of how to design materials by exploiting their coupling. Here, we introduce the concept of ‘polarization twist’, which offers enhanced control over piezoelectric responses in polar materials. Our experimental and theoretical studies provide direct evidence that a ferrielectric perovskite exhibits a large piezoelectric response because of extended polar distortion, accompanied by nonpolar octahedral rotations, as if twisted polarization relaxes under electric fields. The concept underlying the polarization twist opens new possibilities for developing alternative materials in bulk and thin-film forms.

We have investigated the crystal structure of (Bi1/2Na1/2)TiO3–7%BaTiO3 (BNT–7%BT) by high-resolution neutron powder diffraction (NPD) and high-energy synchrotron radiation X-ray diffraction (SR-XRD) analyses. The NPD study revealed that the BNT–7%BT crystals have a single-phase tetragonal structure with P4b m symmetry. The crystal structure refined by the Rietveld method was found to be similar to the ferrielectric P4b m phase reported for BNT at a high temperature of 673 K. The SR-XRD analyses for single crystals of BNT–7%BT demonstrated that the P4b m phase remains as a stable phase in the crystals even after a high electric field is applied for poling, which is different from the structural analysis of ceramics by Ma et al. [Phys. Rev. Lett. 109 (2012) 107602].

A n e w g o l d c l u s t e r c o m p o u n d [Au 23 (NHC ptol ) 6 (CCPh) 9 ] 2+ (NHC ptol = 1,3-di(paramethylbenzyl)benzimidazolin-2-ylidene) (Au 23 NHC ptol ) was synthesized, and its geometric and electronic structures were compared to those of a known phosphine-protected analogue [Au 23 (PPh 3 ) 6 (CCPh) 9 ] 2+ (Au 23 PPh 3 ). Single-crystal X-ray diffraction analysis revealed that Au 23 NHC ptol has a common structural motif with Au 23 PPh 3 : a Au 17 core capped by six NHC ligands and surrounded by three Au 2 (CCPh) 3 oligomers. However, a detailed inspection of the geometric structures elucidated two noticeable differences: (1) the Au 17 core of Au 23 NHC ptol is slightly elongated and sharpened along the C 3 axis compared with that of Au 23 PPh 3 and (2) all of the phenyl rings of the alkynyl ligands in Au 23 NHC ptol face nearly parallel to the equatorial plane of the Au 17 core, whereas randomly aligned phenyl rings are found in Au 23 PPh 3 . Both clusters showed comparable stability at 60 °C in chloroform. UV−vis absorption spectroscopy and differential pulse voltammetry indicated that both clusters exhibit similar electronic structures, but the highest occupied molecular orbital (HOMO) of Au 23 NHC ptol is higher in energy and the HOMO−lowest unoccupied molecular orbital (LUMO) gap of Au 23 NHC ptol is larger compared to Au 23 PPh 3 . Theoretical analysis of the electronic structures showed that the Au 17 core common to both clusters cannot be viewed as a dimer molecule composed of a prolate Au 10 (6e) superatom, but corresponds to a nonspherical superatom with 12 electrons.

Molecular oxygen serves as a useful oxidant for the glycol scission of 1,2-diols and the Hofmann rearrangement of primary amides using pentamethyliodobenzene as a catalyst. The use of isobutyraldehyde and Lewis basic nitriles under O enabled the iodine(i)/(iii) catalytic cycle, where in situ-generated peracid acts as a terminal oxidant.

Surface modification of poly(N-vinyl-2-pyrrolidone)-stabilized gold clusters (1.8 ± 0.6 nm) with aminated cyclodextrins induced aerobic oxidative kinetic resolution of racemic secondary alcohols (krel = 1.2).