High-pressure and environment effects in selenourea and its labile crystal field around molecules

Ambient-pressure trigonal phase α of selenourea SeC(NH2)2 is noncentrosymmetric, with high Z′ = 9. Under high pressure it undergoes several intriguing transformations, depending on the pressure-transmitting medium and the compression or recrystallization process. In glycerine or oil, α-SeC(NH2)2 transforms into phase β at 0.21 GPa; however in water, phase α initially increases its volume and can be compressed to 0.30 GPa due to the formation of α-SeC(NH2)2·xH2O. The single crystals of α-SeC(NH2)2 and of its partial hydrate α-SeC(NH2)2·xH2O are shattered by pressure-induced transitions. Single crystals of phase β-SeC(NH2)2 were in situ grown in a diamond-anvil cell and studied by X-ray diffraction. The monoclinic phase β is centrosymmetric, with Z′ = 2. It is stable to 3.20 GPa at least, but it cannot be recovered at ambient conditions due to strongly strained NH...Se hydrogen bonds. No hydrogen-bonding motifs present in the urea structures have been found in selenourea phases α and β.

Structure, ferroelasticity and Goldilocks zone phase transitions in C3H5N2Al(SO4)2·6H2O

The single crystal growth and sequence of reversible phase transition are described for C3H5N2Al(SO4)2·6H2O. Thermal and structural analyses combined with dielectric studies and optical observations revealed the structural phase transition at T 1 = 339/340 K (I↔II) and T 2 = 347/348 K (II↔III) on heating and cooling, respectively. Both phase transitions are of the first-order type. The symmetry changes from monoclinic to trigonal phase. At 293 K, the large crystals are usually divided into numerous domains of the ferroelastic type that disappear above T 1 on heating and reappear below T 1 on cooling. The domain structure pattern is characteristic for the transition between trigonal and monoclinic phases. The changes of entropy and clear increase of permittivity at T 1 provide evidence for the order–disorder character of this phase transition. The transition at T 2 seems to be displacive.

Identifying a Li-rich superionic conductor from charge–discharge structural evolution study: Li2MnO3

As Li2MnO3 transforms from monoclinic phase to trigonal phase, the diffusion rate of Li ions has been significantly improved.

Construction of 1T-MoS2 quantum dots-interspersed (Bi1−xFex)VO4 heterostructures for electron transport and photocatalytic properties

The present study reports trigonal phase molybdenum disulfide quantum dots (MoS2/QDs)-decorated (Bi1−xFex)VO4 composite heterostructures.

Crystalline structures of Rb2UBr6 ionic conductor determined by neutron diffraction

The neutron powder diffraction technique has been used for structural studies of Rb2UBr6 solid electrolyte as a function of temperature. The low-, room-, and high-temperature structures have been determined. At the temperature range of 4.2–80 K, the compound crystallizes in a monoclinic unit cell in the P21/c space group. At 80 K and 853 K, the compound crystallizes in a tetragonal unit cell in the P4/mnc space group. At 300 K, the lattice constants are a = b = 7.745(1) and c = 11.064(1) Å. At the temperature range of 853–960 K, a trigonal phase is observed in the Pʒ̄ml space group.

Microstructure, XRD and Mössbauer spectroscopy study of Gd doped BiFeO3

The results of fabrication process and characterization of Bi1-xGdxFeO3 (x = 0.05, 0.07, 0.10) ceramics are reported in the paper. The samples were prepared by standard solid state reaction method from the mixture of oxides: Bi2O3, Fe2O3 and Gd2O3. The influence of Gd substitution on the microstructure and density of Bi1-xGdxFeO3 was studied. Phase composition and structure of the obtained samples were investigated by Xray diffraction. It turns out that the Bi1-xGdxFeO3 solid solutions with x = 0.05 and 0.07 crystallize in trigonal structure characteristic of BiFeO3 compound. For the sample with x = 0.1, beside the major trigonal phase, 6% of orthorhombic phase typical for GdFeO3 was detected. Hyperfine interaction parameters were studied by M?ssbauer spectroscopy. M?ssbauer results proved that the spin cycloid characteristic of BiFeO3 compound gradually disappears when substituting Gd3+ ions at the Bi3+ sites.

Computational discovery and characterization of new B2O phases

Our theoretical investigations have unraveled peculiar bonding characters in the current identified superconducting phases for B2O at high pressure, especially the evolution of chemical bonds and electronic states associated with the B12 icosahedral unit in the orthorhombic phase and the pseudo-layered trigonal phase.

Al13Fe3

A new trigonal phase with composition Al13Fe3 (tridecaaluminium triiron) was obtained in the binary Fe–Al diagram by high-pressure sintering (HPS) of a stoichiometric Al3Fe mixture. The refined crystal structure agrees with the descriptions of an unresolved rhombohedral phase reported 30 years ago [Chandrasekaran et al. (1988). Scr. Metall. 22, 797–802]. The structure was refined as an inversion twin with a ratio of 0.506 (18):0.494 (18) for the two twin components.