(Tetra­oxidoselenato-κO)tris­(thio­urea-κS)zinc(II)

The title structure, [Zn(SeO4)(CH4N2S)3], is isomorphous with sulfatotris(thio­urea)zinc(II). In both structures, the Zn2+ cation is coordinated in a tetra­hedral geometry. The corresponding intra­molecular distances are quite similar except for the Se—O and S—O distances. Although the hydrogen-bonding patterns are similar, there are some differences; in the title structure all the H atoms are involved in the hydrogen-bond pattern, in contrast to the situation in sulfatotris(thio­urea)zinc(II). No reproducible anomalies were detected by differential scanning calorimetry in the range 93–463 K until decomposition started at the higher temperature

Tris(2-carbamoylguanidinium) hydrogen fluoro­phospho­nate fluoro­phospho­nate monohydrate

The title structure, 3C2H7N4O+·HFPO3 −·FPO3 2−·H2O, contains three independent 2-carbamoylguanidinium cations, one fluoro­phospho­nate, one hydrogen fluoro­phospho­nate and one water mol­ecule. There are three different layers in the structure that are nearly perpendicular to the c axis. Each layer contains a cation and the layers differ by the respective presence of the water mol­ecule, the hydrogen fluoro­phospho­nate and fluoro­phospho­nate anions. N—H⋯O hydrogen bonds between the guanylurea mol­ecules that inter­connect the mol­ecules within each layer are strong. The layers are inter­connected by strong and weak O—H⋯O hydrogen bonds between the anions and water mol­ecules, respectively. Inter­estingly, the configuration of the layers is quite similar to that observed in 2-carbamoylguanidinium hydrogen fluoro­phospho­nate [Fábry et al. (2012). Acta Cryst. C68, o76–o83]. There is also present a N—H⋯F hydrogen bond in the structure which occurs quite rarely

Dipotassium zinc tetra­iodate(V) dihydrate

The title compound, K2Zn(IO3)4·2H2O, contains two symmetry-independent K and I atoms. These atoms, as well as the Zn atom, are coordinated by shared O atoms and, moreover, the Zn atom is coordinated by two water mol­ecules in trans positions. The K, Zn and water O atoms atoms are situated in special positions on twofold symmetry axes. The hydrogen atoms are involved in strong O—H⋯O hydrogen bonds and O—H⋯I inter­actions also occur. The crystals of the title compound are, in general, twinned, but the sample used for this experiment was free of twinning

N-[Amino(imino)methyl]uronium tetrafluoroborate

In the title compound, C2H7N4O+·BF4 −, inter­molecular N—H⋯O hydrogen bonds connect the cations into chains parallel to the c axis, with graph-set motif C(4). These chains are in turn connected into a three-dimensional network by inter­molecular N—H⋯F hydrogen bonds. The B—F distances distances in the anion are not equal

Properties of BaTiO3 confined in nanoporous Vycor and artificial opal silica

Using the sol-gel technique, BaTiO3 was embedded into nanoporous Vycor and artificial vitreous opal silica for the first time. About 50 vol% of the pores was filled. In case of the Vycor glass (pore diameter 4–6 nm) only amorphous phase was revealed by XRD, IR reflectivity and Raman spectra. After additional gradual annealing, no crystallization was achieved. Chemical reaction with the SiO2 skeleton started at ~1000 K. The room-temperature IR and Raman spectra clearly show characteristic vibrational modes of the ferroelectrically distorted TiO6 octahedra without any long-range order. In case of the opal matrix (densely packed silica spheres, pore diameter up to ~50 nm), crystallization of the ferroelectric BaTiO3 appeared in coexistence with the amorphous phase, but the penetration depth of the crystalline BaTiO3 was limited. From the apparent temperature independence of the effective wide-frequency dielectric response due to the essentially temperature independent effective soft mode stiffened to ~100 cm-1, we can deduce that no macroscopic percolation of the crystalline BaTiO3 has appeared in our opal matrix. Nevertheless, Raman spectra bring evidence of a diffuse ferroelectric phase transition in the opal-BaTiO3 composite