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.

Formation of modified whitlockite-related calcium phosphates under conditions of coprecipitation from aqueous solutions

The features of phase formation during wet coprecipitation from aqueous system Сa2+–NO3––Х (Х – NaH2PO4, Na2HPO4, Na3PO4) at the molar ratio Са2+/РО43–=1.6 and room temperature have been investigated. It was found formation of whitlockite-related calcium phosphates (trigonal system, space group R-3c). The results of elemental analysis indicated the chemical modification of calcium phosphates by sodium cations (samples contained 0.3–0.6 wt.% Na+). According to the resulta of thermogravimetry, the synthesized samples contained up to 6 wt.% of sorption water. Heating of samples to the temperature of 6000C is accompanied by water removal and an increase in particle size from 20–50 nm to 500 nm. It was shown that the use of sodium nitrate as a source of sodium cations in the formation of sodium-containing calcium phosphates allows obtaining compositions of whitlockite- and apatite-related phases. The mass ratio of phases can be adjusted by changing the content of sodium cations in the initial solution. The synthesized samples were characterized by X-ray powder diffraction, thermogravimetry, scanning electron microscopy and FTIR spectroscopy methods. Optimized conditions for preparation of whitlockite-related sodium-containing calcium phosphates as well as composites based on them with apatite-related phase can be further used in the development of materials with the required resorption rate for orthopedics.

Obtaining of luminescent material based on NaBaY(BO3)2 doped with terbium and europium ions

A new luminescent material based on complex borate NaBaY(BO3)2 doped with Tb3+ and Eu3+ ions was obtained by high-temperature solid-state synthesis. Using X-ray diffraction analysis it was shown that NaBaY(BO3)2:0.07Tb3+:0.1Eu3+ crystallizes in trigonal system with the space group R-3m and isotypic with the mineral buetschliit K2Ca(CO3)2. The crystal structure of the phosphor is layered, formed from [BO3] triangles, [YO6] octahedra, [BaO9] and [NaO9] polyhedra. The calculated unit cell parameters for NaBaY(BO3)2:0.07Tb3+:0.1Eu3+ are: a=5.3510(6) Å, c=17.9338(3) Å, V=444.71(2) Å3. The luminescent properties of NaBaY(BO3)2:0.07Tb3+:0.1Eu3+ were studied.

Effects of W6+ substitution on the microwave dielectric properties of Ce2Zr3(MoO4)9 ceramics

Low temperature sintered Ce2Zr3([Formula: see text][Formula: see text][Formula: see text] (marked as CZMW) ceramics were synthesized via the conventional solid-state reaction method. X-ray diffraction results showed that the CZMW ceramics belonged to a Trigonal system with R-3C space group, and without any impure phase formation. The experimental facts revealed that the density and grain morphology greatly affected the microwave dielectric properties. The samples sintered at 825∘C exhibited good microwave dielectric properties: [Formula: see text], [Formula: see text][Formula: see text]GHz (at 11.3[Formula: see text]GHz) and a satisfactory [Formula: see text] ([Formula: see text]1.5[Formula: see text]ppm/∘C) value. It is suggested that the CZMW ceramics are suitable for low-temperature co-fired ceramic (LTCC) applications in microwave devices.

Novel Red-Orange Phosphors Na2BaMg(PO4)2:Pr3+: Synthesis, Crystal Structure and Photoluminescence Performance

A series of new red-orange emission phosphors Na2BaMg(PO4)2:Pr3+ were synthesised by a high-temperature solid-state reaction. The crystal structure and photoluminescence properties of these samples were characterised by X-ray diffraction and spectroscopic measurements. This compound holds P3̅m1 space group of the trigonal system with the lattice parameters of hexagonal cell a=0.5304(3) nm and c=0.6989(3) nm. The phosphor emits the strongest peak at 606 nm when excited by 449 nm. The average Commission Internationale de l’Eclairage chromaticity coordinates calculated for the phosphors are (0.52, 0.46). The results demonstrate the potential application of these phosphors in solid-state lighting and other fields.

Crystal structure of the cobalt human insulin derivative

<p>The structure of the human cobalt insulin derivative at 1.73 Å resolution is described. Single were prepared by the hanging drop vapour diffusion crystallisation method using Zn-free insulin and cobalt(II) acetate.</p>The crystal structure was determined by the single crystal X-ray diffraction method. The investigated insulin derivative exhibits the T₆ form of insulin and crystallizes in the trigonal system in space group <em>R</em>3, with the unit cell parameters <em>a </em>= <em>b </em>= 81.43 Å and <em>c </em>= 33.75 Å. The two cobalt atoms per insulin hexamer and are octahedrally coordinated by three symmetry-related N<em>ε</em>2 atoms of three HisB10/HisD10 and three oxygen atoms from three water molecules.

Trigonal representation of quantum orbitals, from hydrogen to calcium

Inspired from the work of Van Meersshe and Feneau-Dupont (1984), the ternary representation of the basic models in crystallography offers interesting perspectives to illustrate quantum orbitals, the classical S, P, D and F orbitals, by using a 3D representation of a trigonal system in place of the orthogonal system . On the other hand, the studies of the molecular orbitals of orthohydrogen (spins in the same sense) induces the hypothesis of a singularity zone between the atoms of hydrogen which could be a neutral zone favourable to the emergence of neutral particles and potentially can reorganize the repartition of electronic orbitals. Therefore, the nuclear spins can be related to the quantum orbitals distribution. Finally, by associating the ternary system in crystallisation with the orientation of nuclear spins and chemical bonds between the elements, we could work out a "trigonal" representation for the first elements of the periodic table, from hydrogen to calcium. The trigonal approach can facilitate the 3D representation of complex orbital systems. It offers a theoretical potential for crystallographic studies and it can support a large program of experimentation about the formation of the isotopes, the ionic character of covalent bonds and the gas state at low temperature for the electronegative elements of the periodic table.

The New Vanadoborate-supported Hexanuclear Zinc Complex [Zn(teta)]6[(VO)12O6B18O36(OH)6](H2O) · 8H2O

The new vanadoborate-supported zinc complex [Zn(teta)]6[(VO)12O6B18O36(OH)6](H2O) ・8H2O (1, teta = triethylenetetramine) was synthesized hydrothermally and characterized by elemental and thermogravimetric analysis, and IR and UV/Vis spectroscopy. Complex 1 crystallizes in the trigonal system in space group R3̄ and consists of the neutral [Zn(teta)]6[(VO)12O6B18O36(OH)6](H2O) cage aggregate that is built up from a [(VO)12O6B18O36(OH)6]12− cluster decorated with six [Zn(teta)]2+ complex groups, and a water molecule occupying the center of the cluster cage.

Synthesis, Structural Study and Thermal Expansion of Cesium Dititanium Tris(Phosphate)

<p>The new phosphate CsTi₂(PO₄)₃ was synthesized by precipitating method and characterized by scanning electron microscopy with energy-dispersive X-ray microanalyzer, X-ray powder diffraction and IR-spectroscopy. The structure refinement of the phosphate was carried out by a Rietveld analysis. CsTi₂(PO₄)₃ crystallizes with the cubic system (space group <em>Ia</em><em>3</em><em>d</em>), its unit-cell parameters: <em>a</em> = 19.909(5) Å, <em>V</em> = 7892(1) ų. It has the framework structure formed by TiO₆ octahedra and PO₄ tetrahedra, the two type positions of Cs⁺ cations are in the cavities of the structure. CsTi₂(PO₄)₃ structure features are discussed. The results of the undertaken study showed that cesium dititanium tris(phosphate) crystal structure differs from its isoformulic analogues CsZr₂(PO₄)₃ and AM₂(PO₄)₃ (A = Na, K, Rb; M = Ti, Zr), crystallizing in the trigonal system (space group <em>R</em> <em>c</em>) with the kosnarite type. Thermal expansion of the CsTi₂(PO₄)₃ was studied: α<em>_a</em> = 7.85∙10^-6 °C^-1, α<em>_V</em> = 23.5∙10^-6 °C^-1in the range 25–800 °C.</p>