Tracing electron density changes in langbeinite under pressure

Pressure is well known to dramatically alter physical properties and chemical behaviour of materials, much of which is due to the changes in chemical bonding that accompany compression. Though it is relatively easy to comprehend this correlation in the discontinuous compression regime, where phase transformations take place, understanding of the more subtle continuous compression effects is a far greater challenge, requiring insight into the finest details of electron density redistribution. In this study, a detailed examination of quantitative electron density redistribution in the mineral langbeinite was conducted at high pressure. Langbeinite is a potassium magnesium sulfate mineral with the chemical formula [K2Mg2(SO4)3], and crystallizes in the isometric tetartoidal (cubic) system. The mineral is an ore of potassium, occurs in marine evaporite deposits in association with carnallite, halite and sylvite, and gives its name to the langbeinites, a family of substances with the same cubic structure, a tetrahedral anion, and large and small cations. Single-crystal X-ray diffraction data for langbeinite have been collected at ambient pressure and at 1 GPa using a combination of in-house and synchrotron techniques. Experiments were complemented by theoretical calculations within the pressure range up to 40 GPa. On the basis of changes in structural and thermal parameters, all ions in the langbeinite structure can be grouped into `soft' (potassium cations and oxygens) and `hard' (sulfur and magnesium). This analysis emphasizes the importance of atomic basins as a convenient tool to analyse the redistribution of electron density under external stimuli such as pressure or temperature. Gradual reduction of completeness of experimental data accompanying compression did not significantly reduce the quality of structural, electronic and thermal parameters obtained in experimental quantitative charge density analysis.

Pyrochlore-Supergroup Minerals Nomenclature: An Update

The general formula of the pyrochlore-supergroup minerals is A2B2X6Y. The mineral names are composed of two prefixes and one root name (identical to the name of the group). The first prefix refers to the dominant anion (or cation or H2O or vacancy) of the dominant valence at the Y-site. The second prefix refers to the dominant cation of the dominant valence [or H2O or vacancy] at the A-site. Thirty-one pyrochlore-supergroup mineral species are currently distributed into four groups [pyrochlore (B = Nb, X = O), microlite (B = Ta, X = O), roméite (B = Sb5+, X = O), and elsmoreite (B = W, X = O)] and two unassigned members [hydrokenoralstonite (B = Al, X = F) and fluornatrocoulsellite (B = Mg, X = F)]. However, when the new nomenclature system of this supergroup was introduced (2010) only seven mineral species, namely, oxycalciopyrochlore, hydropyrochlore, hydroxykenomicrolite, oxystannomicrolite, oxystibiomicrolite, hydroxycalcioroméite, and hydrokenoelsmoreite, were valid. The seven species belong to the cubic crystal system and space group Fd3¯m and O is predominant in the X structural site. The 24 new mineral species described between 2010 and 2021 are cesiokenopyrochlore, fluorcalciopyrochlore, fluornatropyrochlore, hydrokenopyrochlore, hydroxycalciopyrochlore, hydroxynatropyrochlore, hydroxykenopyrochlore, hydroxymanganopyrochlore, hydroxyplumbopyrochlore, fluorcalciomicrolite, fluornatromicrolite, hydrokenomicrolite, hydroxycalciomicrolite, kenoplumbomicrolite, oxynatromicrolite, oxycalciomicrolite, oxybismutomicrolite, fluorcalcioroméite, hydroxyferroroméite, oxycalcioroméite, oxyplumboroméite, fluornatrocoulsellite, hydrokenoralstonite, and hydroxykenoelsmoreite. Among the new species, hydroxycalciomicrolite belongs to a different space group of the cubic system, i.e., P4232. There are also some mineral species that crystallize in the trigonal system. Hydrokenoelsmoreite occurs as 3C (Fd3¯m) and 6R (R3¯) polytypes. Hydrokenomicrolite occurs as 3C (Fd3¯m) and 3R (R3¯m) polytypes, of which the latter corresponds to the discredited “parabariomicrolite.” Fluornatrocoulsellite crystallizes as 3R (R3¯m) polytype. Surely there are several new pyrochlore-supergroup minerals to be described.

New compound Sm2Ru3Sn5 with a structure derived from Ru3Sn7

Ternary intermetallic compound Sm2Ru3Sn5 was synthesized in the system Sm-Ru-Sn by arc-melting and annealing at 600 °C in the field with high content of Sn. Its crystal structure was determined using single crystal X-ray diffraction data (at 240 K). The compound crystallizes in cubic system with space group I 4 ‾ 3m (No. 217), unit cell parameter is a = 9.4606 (8) Å, Z = 4, Pearson symbol c/40. The intermetallic compound Sm2Ru3Sn5 represents an ordered version of the centrosymmetric Ru3Sn7 structure (space group Im 3 ‾ m), in which 16f Sn-filled crystallographic site is split into two 8c sites, each of which is solely occupied of one sort of atoms – Sn or Sm. The occupation of these two 8c sites leads to a reduction of symmetry due to the removal of the inversion center.

Complex Impedance, Dielectric Properties and Electrical Conduction Mechanism of LaBa0.5Ag0.5FeMnO6 Double Perovskite Oxides

The double perovskite oxide with formula LaBa0.5Ag0.5FeMnO6 was prepared by the sol-gel method. The structural analysis at room temperature indicated that this sample is single phase and crystallize in the cubic system with the Pm-3m space group. The complex impedance spectroscopy has been measured in the range of temperature, 200–340 K, and frequency, 100 Hz–1MHz, respectively. Dielectric measurements by analysis of the impedance function, Z" as a function of Z' versus frequency curves, were mounted to an equivalent circuit consisting of series of combinations of resistor, capacity and constant phase elements. The study of ac conductivity as a function of frequency has been interpreted using the Joncher's law and determines the activation energy. The modulus analysis was also performed indicating the presence of a relaxation process accompanied by a conduction phenomenon.

A number of limit cycle of sextic polynomial differential systems via the averaging theory

The main purpose of this paper is to study the number of limit cycles of sextic polynomial differential systems (SPDS) via the averaging theory which is an extension to the study of cubic polynomial vector fields in (Nonlinear Analysis 66 (2007), 1707--1721), where we provide an accurate upper bound of the maximum number of limit cycles that SPDS can have bifurcating from the period annulus surrounding the origin of a class of cubic system.

MnS/FeS2 heterostructure with high-degree lattice match anchored into carbon skeleton for ultrastable sodium-ion storage

In this work, a heterostructure between MnS and FeS2 featuring identical cubic system and closed lattice parameters confined in one dimensional carbon nanofibers was synthesized through electrospinning technology (denoted as...

A β Ti–20Nb–10Ta–5Zr Alloy with the Surface Structured on the Micro- and Nanoscale

This alloy is shown to be homogeneous (Ti 65%, Nb 20%, Ta 10%, Zr 5%). A change in the elemental composition is observed only in the layer close to the surface with a thickness of about 100 nm. The alloy surface is depleted in titanium (∼20%) and enriched in tantalum (∼20%). There is also a large amount of oxides on the surface (∼50%). The alloy is single-phase with a β-Ti-type crystal lattice (cubic system, space group Im3m). The alloy has yield strength of about 550 MPa and a tensile strength of about 700 MPa. The Young’s modulus is about 50 GPa. The relative elongation of the alloy is about 1.4%. On a microscale, folds and longitudinal comb-like structures up to 0.5 μm in height are found on the surface of wires and plates made of the Ti–20Nb–10Ta–5Zr alloy. When analyzing nanotopology, it is found that, even between comb-like structures or at their tops, there are irregularities up to 100–150 nm in height.

Influence of pairs of alkali metal cations on the formation of complex phosphates at the crystallization of multicomponent self-fluxes

The regularities of phase formation in the systems (МІ1 + МІ2)2O—P2O5—TiO2—МІІO (МІ — Na, K, Rb; MII — Mg, Co, Ni) at the crystallization of multicomponent self-fluxes at the values of molar ratios: (МІ1 + МІ2)/Р = 1.0; Ti/Р = 0.25; MII/Ті = 1.0, and М І 1/М І 2 = 1.0 and 2.0 over the temperature interval of 1000-780 °C have been investigated. For mixed sodium-potassium-phosphate systems, regardless of the ratio of Na/K (1.0 or 2.0), the solidification without crystal formation was found. For Na/Rb-containing systems, the increasing of the so dium amount in the initial melt to the value of molar ratio Na/Rb = 2.0 promoted the crystalization of single crystals of NaTi2(PO4)3 doped by divalent metals ions. In the case of K-Rb-phosphate self-fluxes, it was found that the value of K/Rb = 2.0 is optimal for the growing of langbeinite-related single crystals (K/Rb)2MII0,5Ti1,5(PO4)3 (MII — Mg, Co, Ni) which belong to cubic system (space group P213). The calculated cell parameters for new phosphates (K/Rb)2MII 0.5Ti1.5(PO4)3 depend on the nature of MII: a = 9.851(6) Å for Mg, a = 9.853(9) Å for Co and a = 9.850 (1) - for Ni. In the FTIR spectra of phosphates (K/Rb)2MII0.5Ti1.5(PO4)3, the characteristic modes in the region of 520-650 сm–1 and 1000-1250 сm-1 which have been assigned to symmetric and asymmetric stretching vibrations (ν4, ν1 and ν3) of phosphate tetrahedron confirmed the presence of orthophosphate type anion in their composition. According to results of thermal analysis, the melting points of (K/Rb)2MII0.5Ti1.5(PO4)3 are at a temperatures of 1082 °С for MII — Ni, 1057 °С for MII — Co, and above 1100 °С for MII — Mg. The synthesized complex phosphates have been investigated using the powder X-Ray diffraction method, thermogravimetry, differential thermal analysis, and FTIR-spectroscopy.

Untersuchungen zur Polymorphie der Cäsium-Dodekahalogeno-closo-Dodekaborate Cs2[B12X12] (X = Cl–I)

Thermoanalytic DSC and temperature-dependent X-ray diffraction investigations on the cesium dodecahalogeno-closo-dodecaborates Cs2[B12X12] (X = Cl–I) have revealed solid-solid phase transitions from their trigonal room-temperature α-forms (e.g. α-Cs2[B12Cl12]: a = 959.67(3) pm, c = 4564.2(2) pm, Z = 6, space group R$\overline{3}$) into cubic high-temperature modifications. The isotypic title compounds crystallize in the space group Pm$\overline{3}$n (e.g. β-Cs2[B12Cl12]: a = 1051.98(6) pm, Z = 2) with a W3O-type defect structure. The statistic occupation of six possible positions with only four Cs+ cations results in a cation-deficient A2B arrangement for Cs2[B12X12]. Upon cooling the β-phase, a third polymorph was observed, which also crystallizes in the cubic system, but now in the space group Ia$\overline{3}$d (e.g. γ-Cs2[B12Cl12]: a = 2102.2(3) pm, Z = 16), and has to be regarded as a phase with only a partially disordered cation substructure. In this crystal structure the [B12X12]2− anions exhibit a NaTl-type arrangement, in which the Cs+ cations occupy suitable interstices. The phase transitions of the differently halogenated cesium salts follow no specific trend as the transition from the trigonal α- to the cubic β-form occurs at 178 °C for the chlorinated, at 270 °C for the iodinated and at 325 °C for the brominated examples. On further heating however, β-Cs2[B12I12] starts to decompose at 945 °C first, followed by β-Cs2[B12Br12] and β-Cs2[B12Cl12] at 959 °C and 983 °C, respectively.

FORMATION POSSIBILITY OF THE AL3SI METASTABLE PHASE DURING ION-BEAM AND MAGNETRON DEPOSITION OF COMPOSITE AL-SI FILMS

Metastable phases such as Al3Si can form in Al-Si composite films obtained by magnetron and ion-beam sputtering. In this work, we investigated the stability region of the Al3Si phase depending on the composition of the ion-beam AlxSi1-x films. Using X-ray diffraction and Ultrasoft X-ray Emission Spectroscopy, an ordered Al3Si solution with a primitive unit cell of the cubic system Pm3m and a lattice parameter of 4.085 Å was found in Al1-xSix ionbeam films. Studies have shown that the long-range order is quite resistant to changes in the elemental composition.