Inorganic perovskite ferroelectrics are widely used in nonvolatile memory elements, capacitors, and sensors because of their excellent ferroelectric and other properties. Organic ferroelectrics are desirable for their mechanical flexibility, low weight, environmentally friendly processing, and low processing temperatures. Although almost a century has passed since the first ferroelectric, Rochelle salt, was discovered, examples of highly desirable organic perovskite ferroelectrics are lacking. We found a family of metal-free organic perovskite ferroelectrics with the characteristic three-dimensional structure, among which MDABCO (-methyl--diazabicyclo[2.2.2]octonium)-ammonium triiodide has a spontaneous polarization of 22 microcoulombs per square centimeter [close to that of barium titanate (BTO)], a high phase transition temperature of 448 kelvins (above that of BTO), and eight possible polarization directions. These attributes make it attractive for use in flexible devices, soft robotics, biomedical devices, and other applications.

Molecular piezoelectrics are highly desirable for their easy and environment-friendly processing, light weight, low processing temperature, and mechanical flexibility. However, although 136 years have passed since the discovery in 1880 of the piezoelectric effect, molecular piezoelectrics with a piezoelectric coefficient comparable with piezoceramics such as barium titanate (BTO; ~190 picocoulombs per newton) have not been found. We show that trimethylchloromethyl ammonium trichloromanganese(II), an organic-inorganic perovskite ferroelectric crystal processed from aqueous solution, has a large of 185 picocoulombs per newton and a high phase-transition temperature of 406 kelvin (K) (16 K above that of BTO). This makes it a competitive candidate for medical, micromechanical, and biomechanical applications.

Tetrazole compounds have been studied for more than one hundred years and applied in various areas. Several years ago Sharpless and his co-workers reported an environmentally friendly process for the preparation of 5-substituted 1H-tetrazoles in water with zinc salt as catalysts. To reveal the exact role of the zinc salt in this reaction, a series of hydrothermal reactions aimed at trapping and characterizing the solid intermediates were investigated. This study allowed us to obtain a myriad interesting metal-organic coordination polymers that not only partially showed the role of the metal species in the synthesis of tetrazole compounds but also provided a class of complexes displaying interesting chemical and physical properties such as second harmonic generation (SHG), fluorescence, ferroelectric and dielectric behaviors. In this tutorial review, we will mainly focus on tetrazole coordination compounds synthesized by in situ hydrothermal methods. First, we will discuss the synthesis and crystal structures of these compounds. Their various properties will be mentioned and we will show the applications of tetrazole coordination compounds in organic synthesis. Finally, we will outline some expectations in this area of chemistry. The direct coordination chemistry of tetrazoles to metal ions and in situ synthesis of tetrazole through cycloaddition between organotin azide and organic cyano group will be not discussed in this review.

Semiconducting ferroelectricity is realized in hybrid perovskite-type compounds (cyclohexylammonium)2 PbBr4-4 x I4 x (x = 0-1). By adjusting the composition x, the bandgap is successfully tuned from previously reported 3.65 eV to as low as 2.74 eV, and the excellent ferroelectricity was kept intact. This finding may contribute to improving the photoelectronic and/or photovoltaic performance of hybrid perovskite-type compounds.

The inclusion compound [(CH3)2NH2]2[KCo(CN)6] exhibits a marked temperature-dependent dielectric constant and can be considered as a model of tunable and switchable dielectric materials. Crystal structure and solid-state NMR studies reveal a switchable property between low and high dielectric states around 245 K. This originates from an order-disorder phase transition of the system, changing the dynamics of the polar dimethylammonium (DMA) cation. Furthermore, the tuning of the dielectric constant at temperatures below the phase transition point is related to increasing angular pretransitional fluctuations of the dipole moment of DMA.

Coupling of ferroelectricity and optical properties has become an interesting aspect of material research. The switchable spontaneous polarization in ferroelectrics provides an alternative way to manipulate the light-matter interaction. The recent observation of strong photoluminescence emission in ferroelectric hybrid organic-inorganic compounds, (pyrrolidinium)MnX3 (X = Cl or Br), is an attractive approach to high efficiency luminescence with the advantages of ferroelectricity. However, (pyrrolidinium)MnX3 only displays ferroelectricity near or below room temperature, which limits its future applications in optoelectronics and multifunctional devices. Here, we rationally designed and synthesized high-temperature luminescent ferroelectric materials. The new hybrid compound (3-pyrrolinium)MnCl3 has a very high Curie temperature, Tc = 376 K, large spontaneous electronic polarization of 6.2 μC/cm(2), and high fatigue resistance, as well as high emission efficiency of 28%. This finding is a further step to the practical use of ferroelectric luminescence based on organic-inorganic compounds.

Microsymposia C149 MS given in this presentation with results obtained with an ultrastable double aberration-corrected and monochromated electron microscope. First of all, we will demonstrate the detection of low-loss features in plasmonic nanostructures down to the infrared part of the electron energy loss spectrum by directly imaging resonances down to 0.5eV, the lowest features currently detected with EELS [1]. Using momentum resolved near-edge structures we will discuss the detection of the strong anisotropy in bonding in carbon nanotubes. After an overview of the imaging conditions used to detect ordering changes in alloy nanoparticles using a combination of X-ray diffraction techniques and high-angle annular dark-field STEM imaging and simulations, we will discuss the study the application of atomic-resolved EELS mapping in the study of interfaces [2], [3]. We will demonstrate how this powerful technique can be used in the study of the structure and substitutional effects on the atomic structure of interfaces and electronic states changes within one or two unit cells from the interface. We will demonstrate how such spectroscopic technique can be used to detect changes in valence and electronic structure as well as the termination of substrate surfaces in contact with epitaxial films. Examples will show how the stability of microscopes, coupled with atomic resolution, can be used to not only obtain spectroscopic information but aso to determine, directly from high angle annular dark-field images, the local strain at interfaces and at dislocations [4]. Additional examples will highlight the application of microscopy technique to the analysis of clusters, multiferroic materials based on the perovskite structures, and interfaces in complex oxides. These examples demonstrate that compositional and chemical state (valence and coordination) information can be obtained down to the Ångstrom level. Silica nanowires (SiO x-NWs) embedded with Au peapods have been studied by energy-filtered scanning transmission electron microscopy (EFTEM), Au L 3-and O K-edge x-ray absorption near-edge structure (XANES) and x-ray emission spectroscopy (XES). XANES and XES data show that band gaps of Au-peapod embedded and pure SiO x-NWs were 6.8 eV. XANES results indicate illumination induced electron transfer from Au peapod to SiO x-NWs. Photo-response and EFTEM measurements show that green light has more significant enhancement of photo conductivity than red and blue light due to surface plasmon resonance.

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