Влияние дейтерирования на фазовые переходы в (NH-=SUB=-4-=/SUB=-)-=SUB=-3-=/SUB=-VOF-=SUB=-5-=/SUB=-

The (ND4)3VOF5 crystal was grown with a high degree of deuteration (D ~ 92%). Structural and thermophysical studies have been carried out, the parameters of phase transitions have been determined. It was found that the deuteration of the ammonium cation in (NH4)3VOF5 led to a change in the chemical pressure, which was accompanied by an increase in the unit cell volume and an increase in the phase transition temperatures. The baric coefficients dTi / dp were determined and the phase T-p diagram (ND4)3VOF5 was constructed. A decrease in the temperature stability of the initial cubic phase Fm 3m in (ND4)3VOF5, as well as a wedging out of the intermediate monoclinic phase at a lower pressure as compared to (NH4)3VOF5, was found.

Химическое сжатие, структурная нестабильность и ИК-активные фононы в ряду редкоземельных аналогов францисита Cu-=SUB=-3-=/SUB=-RE(SeO-=SUB=-3-=/SUB=-)-=SUB=-2-=/SUB=-O-=SUB=-2-=/SUB=-Cl

ATR and transmission spectra of a series of rare-earth francisite-like phases Cu3RE(SeO3)2O2Cl (RE is a rare earth element, RE = Nd, Sm, Eu, Gd, Dy, Ho, Tm, Yb) were studied. The frequencies of the IR-active phonons of the crystals under study were determined. In the dependences of phonon frequencies on the ionic radius in a series of isostructural compounds, two tendencies are observed: a hardening of frequencies due to an increase in chemical pressure and a softening of the vibration frequencies, in which rare-earth ions are involved, due to an increase in the mass of a specific rare-earth ion. In the Cu3Dy(SeO3)2O2Cl crystal, an anomalous softening of low-frequency phonons at low temperatures was observed, which was apparently associated with the structural instability of the compound.

Tutorial on Chemical Pressure Analysis: How Atomic Packing Drives Laves/Zintl Intergrowth in K3Au5Tl

The tight atomic packing generally exhibited by alloys and intermetallics can create the impression of their being composed of hard spheres arranged to maximize their density. As such, the atomic size factor has historically been central to explanations of the structural chemistry of these systems. However, the role atomic size plays structurally has traditionally been inferred from empirical considerations. The recently developed DFT-Chemical Pressure (CP) analysis has opened a path to investigating these effects with theory. In this article, we provide a step-by-step tutorial on the DFT-CP method for non-specialists, along with advances in the approach that broaden its applicability. A new version of the CP software package is introduced, which features an interactive system that guides the user in preparing the necessary electronic structure data and generating the CP scheme, with the results being readily visualized with a web browser (and easily incorporated into websites). For demonstration purposes, we investigate the origins of the crystal structure of K3Au5Tl, which represents an intergrowth of Laves and Zintl phase domains. Here, CP analysis reveals that the intergrowth is supported by complementary CP features of NaTl-type KTl and MgCu2-type KAu2 phases. In this way, K3Au5Tl exemplifies how CP effects can drive the merging for geometrical motifs derived from different families of intermetallics through a mechanism referred to as epitaxial stabilization.