Organic–inorganic perovskites are a class of interesting compound in the perovskite family due to their unique structures of alternately stacking sheets of organic and inorganic components on the molecular scale. In this highlight, the basic knowledge and recent advances in organic–inorganic perovskites are reviewed with particular emphasis on the feature work including: the novel - and -oriented perovskite structures, synthesis, film preparation, patterning methods and optoelectronic properties of hybrid perovskites. Moreover, the small functional organic molecules can be templated into a regular arrangement by the inorganic perovskite framework. This unique material with nature-formed lamellar structure has the potential to be used as a template to create novel derivatives and bring about unique physical properties. Some interesting examples, such as intercalated polymer and silica network by topochemical polymerisation, fabrication of disk-like semiconductor nanocrystals and metal nanoparticles by hybrid perovskite templates are described.

Layered organic-inorganic hybrid perovskites: structure, optical properties, film preparation, patterning and templating engineering

Mott insulators are identified here with ordinary magnetic insulators. The insulating gap, local moment, and effective spin hamiltonian aspects are qualitatively explained by means of a novel set of solutions of the Hartree-Fock equations. The apparent conflict between Bloch's theorem and localized-electron phenomenology is thereby resolved in an elementary manner. This Hartree-Fock approach also sheds considerable light on the physical mechanisms responsible for the associated metal-insulator (Mott) and other related phase transitions, as observed in V2O3 and several other materials. With some generalizations and refinements, this theoretical picture is shown to also account semiquantitatively for a number of detailed properties of NiO and CoO, two of the most extensively studied Mott insulator materials. A wide variety of experimental data for NiO is surveyed in order to determine reasonable values for its effective Hubbard hamiltonian parameters, suitably generalized for the 3d electrons. The ...

Electronic structure of Mott insulators

Local and cooperative Jahn-Teller interactions in model structures

The synthesis of Co5(OH)8(C7H15CO2)2·4H2O, Co5(OH)8(O2CC6H12CO2)·5H2O, Co5(OH)8(C12H25SO4)2·(3H2O·2NH3), and Co5(OH)8(C2N3)2·6H2O, their characterization by electron microscopy, XRD, TGA, IR, UV−vis, and XANES, and their magnetic properties are reported. They belong to a family of layered compounds having a triangular magnetic lattice. The basal spacing is 22.8, 16.2, 25.0, and 11.5 A for the carboxylate, dicarboxylate, sulfate, and cyanide, respectively. From the powder X-ray and crystal electron diffraction data, the compounds are inferred to adopt the structure of the monoclinic form of Zn5(OH)8X2·solvent. XANES confirms that only divalent cobalt is present in the compounds and visible absorption spectra display bands originating from both octahedral and tetrahedral coordinated CoII and none from CoIII. The magnetic data show that all the compounds behave as two sublattice ferrimagnets which are characterized by a minimum in the temperature dependence of the moments and long-range ordering observed by ...

Hard magnets based on layered cobalt hydroxide: The importance of dipolar interaction for long-range magnetic ordering

Profile analysis of powder neutron diffraction data: Its scope, limitations, and applications in solid state chemistry

The optical absorption spectrum of the ferromagnetic insulator ${\mathrm{K}}_{2}$Cr${\mathrm{Cl}}_{4}$ has been measured from 8000 to 25 000 ${\mathrm{cm}}^{\ensuremath{-}1}$ and for temperatures between 4.2 and 300\ifmmode^\circ\else\textdegree\fi{}K.

Optical Properties of Ferromagnetic K 2 Cr Cl 4

The crystal and magnetic structure, and the temperature variation of the moment, of Rb 2 CrCl 4 have been investigated using neutron diffraction. The Cr 2+ , S = 2, spins order ferromagnetically at T c = 57 ± 2 K. At 4.2 K they lie perpendicular to the tetragonal axis with a moment of 3.7 ± 0.4 μ B /ion. As the temperature is raised the moment falls rapidly in a manner characteristics of a two-dimensional easy-plane ferromagnet.

A. K. Gregson

Papers

Optical Properties of Ferromagnetic K 2 Cr Cl 4

Neutron scattering study of the magnetism of Rb2CrCl4, a two-dimensional easy-plane ferromagnet

Neutron diffraction study of the crystal and magnetic structure of the ionic ferromagnet Cs2CrCl4

The magnetic properties of CsCrCl3, an antiferromagnetic chain compound with single-ion anisotropy