Bismuth substituted calcium,strontium, and lead apatites

Bismuth substituted apatites of two general types have been prepared: M_10?2xBi_xNa_x(PO₄)₆Y₂ (M = Ca, Sr, Pb; Y = F, Cl) and lead apatites with the Y ion completely vacant Pb_10?(2x+2)BixNa_x+2(PO₄)₆. X-ray powder diffraction patterns of all the compounds show the $\text{P6}{}_3\text{m}$ hexagonal apatite type structure. The change of the lattice parameters and $\text{c}\text{a}$ values with compositions indicate the preference of the bismuth ions to occupy the 6h triangular positions. Bi³⁺ tends to incorporate in apatites with unoccupied halide positions.     

Nd3+, Eu3+, and Gd3+ ions as local probes in the NaxSr3−2xLnx(PO4)2 and KCaLn(PO4)2 rare earth phosphates

Use of Nd³⁺, Eu³⁺, and Gd³⁺ as local structural probes allows the determination of the rare earth positions in the Na_xSr_3?2xLn_x(PO₄)₂ (Ln = La to Tb) and KCaLn(PO₄)₂ phases (Ln = rare earth). Moreover, a common feature of both series is a particularly high splitting of the excitation ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and ${}^6\text{P}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ levels of the Gd³⁺ ions.     

Infrarotspektroskopische und röntgenographische Untersuchungen von Bleihydroxylapatit,Bleioxyapatit und Bleialkaliapatiten

The infrared spectra of lead hydroxyapatite Pb₁₀(PO₄)₆(OH)₂, oxyapatite Pb₁₀(PO₄)₆O, and the lead alkaliapatites Pb₈M₂(PO₄)₆ (M = Na, K, Rb, T1) were investigated down to 200 cm^?1. There are significant differences between all these spectra. In the hydroxy- and oxyapatite spectrum one band is ascribed to the translational motion of the OH^? and O^2? ions, respectively. The thermal dependance of the dehydration of hydroxy to oxyapatite was studied by X-ray methods, both compounds forming a solid solution. The heat of decomposition of hydroxyapatite was found to be ΔH = 5 kcal/mole. Moreover, complete miscibilities could be shown to exist in the systems $\text{Pb}{}_8\text{Na}{}_2\text{(PO}{}_4\text{)}{}_6\text{Pb}{}_{10}\text{(PO}{}_4\text{)}{}_6\text{O}$ and $\text{Pb}{}_8\text{Na}{}_2\text{(PO}{}_4\text{)}{}_6\text{Pb}{}_{10}\text{(PO}{}_4\text{)}{}_6\text{(OH)}{}_2$, respectively.     

Substitution in barium-fluoride apatite: The crystal structures of Ba10(PO4)6F2, Ba6La2Na2(PO4)6F2 and Ba4Nd3Na3(PO4)6F2

The crystal structures of the apatites Ba₁₀(PO₄)₆F₂(I), Ba₆La₂Na₂(PO₄)₆F₂(II) and Ba₄Nd₃Na₃(PO₄)₆F₂ (III) have been determined by single-crystal X-ray diffraction. All three compounds crystallize in a hexagonal apatite-like structure. The unit cells and space groups are: I, a = 10.153(2), c = 7.733(1)Å, $\text{P6}{}_3\text{m}\text{; a = 9.9392(4), c = 7.4419(5)}$Å, $\text{P}\text{6}$; III, a = 9.786(2), c = 7.281(1)Å, $\text{P}\text{3}$. The structures were refined by normal full-matrix crystallographic least squares techniques. The final values of the refinement indicators R_w and R are: I, R_w = 0.026, R = 0.027, 613 observed reflections; II, R_w = 0.081, R = 0.074, 579 observed reflections; III, R_w = 0.062, R = 0.044, 1262 observed reflections.In I, the Ba(1) atoms located in columns on threefold axes, are coordinated to nine oxygen atoms; the Ba(2) sites form triangles about the F site and are coordinated to six oxygen atoms and one fluoride ion. The fluoride ions are statistically displaced ～0.25 Å from the Ba(2) triangles. This displacement of the F ions is analogous to the displacement of OH ion in Ca₁₀(PO₄)₆(OH)₂.The structures of II and III contain disordered cations. In II there is disorder between La and Na in the column cation sites as well as triangle sites. In III, Nd and Na ions are ordered in the column sites, but there is disorder among Ba and the remaining Nd and Na ions in the triangle sites to give an average site population of $\text{2}\text{3}\text{Ba}\text{,}\text{1}\text{6}\text{Nd}\text{,}\text{1}\text{6}\text{Na}$. The coordination of the rare earth ions and Na ions in the ordered column sites are nine and six oxygens, respectively, in accord with the greater charge of the rare earth ions as compared with Na. The F ions in both II and III suffer from considerable disorder in position, and their locations are not precisely known.     

Synthèse et caractéristiques cristallographiques des phases solides de type fluorine des systèmes PbF2LnF3

A preliminary study of the PbF₂LnF₃ systems (Ln = lanthanides and Y) has allowed the characterisation of three phases: a disordered fluorite-like solid solution Pb_1?xLn_xF_2+x the domain of which increases with increasing temperature and dopant ion radius, and two anion-excess fluorite related superstructures: Pb₂YF₇ (tetragonal, space group I4 or $\text{I4}\text{m}\text{, a \#}\text{a}{}_{\mathrm{<mtext>F</mtext>}}\text{√2}\text{, c \# 3a}{}_{\mathrm{<mtext>F</mtext>}}$) and Pb₄Ln₃F₁₇ with Ln = SmLu (rhombohedral, space group $\text{R3, a}{}_{\mathrm{<mtext>h</mtext>}}\text{\# (}\text{a}{}_{\mathrm{<mtext>F</mtext>}}\text{√2}\text{)√7, c}{}_{\mathrm{<mtext>h</mtext>}}\text{\# 2a}{}_{\mathrm{<mtext>F</mtext>}}\text{√3}$). The crystallographic characteristics of the two ordered phases have been confirmed by electron diffraction.     

Etude des equilibres solide-liquide des systems MIPO3Sm(PO3)3 (MI = Li,Na, Ag)

The M^IPO₃Sm(PO₃)₃(M^I = Li, Na, Ag) systems were studied. Differential thermal analysis and X-ray diffraction were used to investigate the liquidus and solidus relations. Three compounds LiSm(PO₃)₄, NaSm(PO₃)₄, and AgSm(PO₃)₄ were obtained which melt incongruently at 1248, 1143, and 1078 K, respectively. These compounds are isomorphous with their homologs LiLn(PO₃)₄, NaLn(PO₃)₄, AgLn(PO₃)₄ (Ln = Ce, La, Nd). They belong to the monoclinic system. The LiSm(PO₃)₄ unit cell parameters refined by least squares method are a = 16.43(3) Å, b = 7.16(1) Å, c = 9.65(3) Å, β = 125,9°(1), with the space group $\text{C2}\text{c}$ and Z = 4. NaSm(PO₃)₄ and AgSm(PO₃)₄ are isotypic; they cristallize in the $\text{P2}{}_1\text{c}$ space group, Z = 4; their unit cell parameters are, respectively, a = 12.18(1) Å, b = 13.05(1) Å, c = 7.25(5) Å, β = 126,53°(4), $\text{a = 12.25(1)}\text{A}\text{?}$, b = 13.06(1) Å, c = 7.201(9) Å, β = 126,57°(7). The ir spectra of the last two compounds indicate that these phosphates are chain phosphates.     

Apatites of divalent europium

The preparation methods of Eu₃(PO₄)₂, Eu₅(PO₄)₃F, Eu₃(PO₄)Cl and Eu₅(AsO₄)₃OH are described. Eu₃(PO₄)₂ crystallizes in a rhombohedral unit cell and the apatite like compounds in the $\text{P6}{}_3\text{m}$ hexagonal structure. All the compounds are isomorphous with the corresponding Sr compounds, and similar in size. Magnetic susceptibility measurements show that Eu₃(PO₄)₂ is magnetically ordered below 5 K and Eu₅(PO₄)₃F and Eu₅(PO₄)₃Cl are paramagnetic. Solid solution of the Eu_5?xCa_x(PO₄)₃F system obey Vegard's law, while the Eu_5?xBa_x(PO₄)₃F and Eu_5?xBa_x(PO₄)₃Cl systems show a trend to form ordered solid solutions.     

Rare earth substituted fluoride-phosphate apatites

Compositions with the general formula Ln_xM_10?2xNa_x(PO₄)₆F₂ (Ln = La, Pi, Nd, Sm, Eu, Dy, Er, Lu, andY;M = Ca, Sr, and Ba) have been prepared and studied by X-ray diffraction methods. The hexagonal apatite like structure was indicated by the powder patterns of all the compounds (with Ba compounds only when Ln = La through Sm). Single crystal precession data reveal that the crystal lattice of all the compositions in the Ca and Sr system have space group P6₃/m, the Ln₂Ba₆Na₂(PO₄)₆F₂ compounds crystallize in space group P6 and the Ln₃Ba₄Na₃(PO₄)₆F₂ compounds in the trigonal space group P3. Order and disorder mechanisms of the substitution and its dependence on size and polarization effects are discussed.     

Solid solutions of Pb8M2(XO4)6 lead alkali apatites

The Pb₈Na_2?xK_x(PO₄)₆, Pb₈Na_2?xK_x(AsO₄)₆, Pb₈Na_2?xRb_x(PO₄)₆, and Pb₈K_2?xRb_x(PO₄)₆ systems were studied. The compounds crystallize at all compositions in the P6₃m hexagonal apatite structure and form true solid solutions. The change of the lattice parameters of the composition and of the c/a values and their relation to the ionic radii of the alkali ions are discussed.     

Les phases SrLnMnO4 (Ln = La,Nd, Sm,Gd), BaLnMnO4 (Ln = La,Nd) et M1+xLa1−xMnO4 (M = Sr,Ba)

The phases SrLnMnO₄ (Ln = La, Nd, Sm, Gd), BaLnMnO₄ (Ln = La, Nd) and the solid solutions M_1+xLa_1?xMnO₄ (M = Sr: 0 ? x ? 1; M = Ba: 0 ? x ? 0.50) have a K₂NiF₄-type structure. The $\text{c}\text{a}$ ratio of the unit cell is related to the electronic configuration of the Mn³⁺ ions.     

Crystal structures of phosphomolybdyl salts: Pb(MoO2)2(PO4)2 and Ba(MoO2)2(PO4)2

Crystal structures of Pb(MoO₂)₂(PO₄)₂ and Ba(MoO₂)₂(PO₄)₂ were determined. Both compounds contain the molybdyl group MoO₂. The monoclinic unit-cell parameters are a = 6.353(7), b = 12.289(4), c = 11.800 Å, β = 92°56(6), and Z = 4 for the lead salt and a = 6.383(8), b = 7.142(7), c = 9.953(8) Å, β = 95°46(8), and Z = 2 for the barium salt. $\text{P2}{}_1\text{c}$ is the common space group. The R values are respectively R = 0.027 and R = 0.031 for 1964 and 1714 independent reflections. The frameworks built up by a three-dimensional network of monophosphate PO₄ and molybdyl MoO₂ groups are similar, characterized mainly by corner-sharing PO₄ and MoO₆ polyhedra. Two oxygen atoms of each MoO₆ group are bonded to the molybdenum atom only as in other molybdyl salts.     

Ln(GaM2+)O4 and Ln(AlMn2+)O4 compounds having a layer structure [Ln = Lu,Yb, Tm,Er, Ho,and Y,and M = Mg,Mn, Co,Cu, and Zn]

A series of new compounds Ln(GaM²⁺)O₄ and Ln(AlMn²⁺)O₄ having a layer structure were successfully prepared [Ln = Lu, Yb, Tm, Er, Ho, and Y, and M = Mg, Mn, Co, Cu, and Zn]. The synthesis conditions and the unit cell parameters for 23 compounds have been determined. These compounds are isostructural with YbFe₂O₄ (space group $\text{R}\text{3}\text{m, a = 3.455(1)}$ Å, and c = 25.109(2) Å).     

Oxydes de type perovskite du systeme CaNbO

Three perovskite-like phases of the CaNbO system have been isolated, $\text{Ca}{}_{\mathrm{x}}\text{NbO}{}_3\text{(0.9 ? x ? 1),}\text{Ca(Ca}{}_{\mathrm{x}}\text{Nb}{}_{\mathrm{1?x}}\text{)}\text{O}{}_3\text{(0 ? x ?}\text{1}\text{3}\text{)}$, and Ca₃Nb₂O_8?x. X-ray powder diffraction and electron microscopy and diffraction were used to obtain crystallographic data of these phases. The high temperature form of Ca(Ca_xNb_1?x)O₃ perovskites, where calcium ions occupy partially the octahedral sites, presents an orthorhombic symmetry and quasi-periodic twin bands like Ca_xNbO₃ compounds. Two monoclinic forms (for $\text{x =}\text{1}\text{3}$ and $\text{x =}\text{1}\text{4}$) were found by heating Ca(Ca_xNb_1?x)O₃ compounds at lower temperature for long periods; ordering of calcium and niobium ions in octahedral sites is proposed for that structure. The Ca₃Nb₂O_8?x compound presents a quadratic cell: ordering of the cations derived from (NH₄)₃FeF₆ structure is proposed in agreement with the observed space group $\text{P4}\text{nnc}$. A new multiple-phase family, with general formula Ca_nNb_nO_3n+2, was obtained for n = 4.25, 4.5, and 5; electron microscopy shows intergrowth phenomena.     

The crystal structure of cobalt orthophosphate Co3(PO4)2

The crystal structure of cobalt orthophosphate has been refined by full-matrix least-squares procedures using automatic diffractometer data to a residual R = 0.039 (R_w = 0.058). The space group is $\text{P2}{}_{\mathrm{l}}\text{c}$, with a = 5.063(1), b = 8.361(2), c = 8.788(2) Å, and β = 121.00(2)°. Co₃(PO₄)₂ is isotypic with the previously reported γ-Zn₃(PO₄)₂ and Mg₃(PO₄)₂. Cobalt ions occupy two distinct coordination polyhedra, one five and one six-coordinated, in a ratio of two to one. The structure is described in detail.     

Transition metal iodates. VI. Preparation and characterization of the larger lanthanide iodates

In the continuation of this work, the Ln^III(IO₃)₃xH₂O type N compounds (abbreviated x_N) of La through Sm were prepared by precipitation, thermal decomposition, and by crystallization from the gel, from ambient and boiling water, and from boiling HNO₃. A total of 36 different compounds with 6 ? x ? 0 were obtained occurring in 12 structural types including one amorphous; in addition La₅(IO₆)₃ and four isostructural double salts of the type Ln(IO₃)₃·HIO₃ were obtained.Characterization techniques used included powder X-ray diffraction, differential thermal analysis, thermogravimetric analysis, second harmonic generation, and infrared spectroscopy.Out of the total of 16 crystalline iodate structures occurring for all the lanthanides, single crystals were obtainable in 11, comprising a total of 54 compounds.Including all the lanthanides (plus Y, less Pm), the x_N groups of isostructural compounds, with the number of compounds in parentheses, were the following: 6(1), 5_I(4), 5_II(2), 4(9), amorphous with 5 ? x ? 0 (15), 2_I(3), 2_II(9), 1(4), $\text{1}\text{2}\text{(2)}$, O_I(14), O_II(2), O_III(4), O_IV(3), O_V(4), and O_VI(1).     

Synthesis and structural study of the new rare earth magnesium borates LnMgB5O10 (Ln = La, …, Er)

To obtain rare earth luminescent materials with weak concentration quenching, the B₂O₃-rich portion of the ternary diagram Ln₂O₃MgOB₂O₃ (Ln = rare earth) has been investigated. A ternary phase of composition LnMgB₅O₁₀ has been found for Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er. These compounds all crystallize in the monoclinic space group $\text{P2}{}_1\text{c}$. The structure has been determined on a LaMgB₅O₁₀ crystal. A full-matrix least-squares refinement leads to R = 0.039. The structure can be described as being made of (B₅O₁₀^5?)_n two-dimensional layers linked together by the lanthanum and magnesium ions. The rare earth atom coordination polyhedra form isolated chains. These borates are isostructural with some rare earth cobalt borates.     

Nouveaux thiochlorures de molybdène(II): Mo6Cl10Y (Y = S,Se, Te): Structure et propriétés magnétiques et électriques

The thiochlorides Mo₆Cl₁₀Y (Y = S, Se, Te) have been prepared; they are isostructural with Nb₆I₁₁, space group Pccn, and have four formula units per unit cell. The X-ray structure of Mo₆Cl₁₀Se has been determined from three-dimensional single-crystal counter data and refined to a final R value of 0.053 for 3350 independent reflections. The most important result concerning this structure is a statistical distribution of the Se atom on the unit (Mo₆X′₈) with $\text{X′ ?}\text{7}\text{8}\text{Cl}\text{+}\text{1}\text{8}\text{Se}$: so the compound Mo₆Cl₁₀Se must be formulated $\text{(Mo}{}_6\text{Cl}{}_7\text{Se)Cl}{}_{\mathrm{<mtext>4</mtext><mtext>2</mtext>}}\text{Cl}{}_{\mathrm{<mtext>2</mtext><mtext>2</mtext>}}$. The diamagnetic and dielectric behavior of these new thiochlorides is discussed.     

An X-ray and neutron powder diffraction study of the Ca2+xNd8−x(SiO4)6O2−0.5x system

The variation in lattice parameters with bulk composition and preparation temperature has been determined from X-ray powder diffraction data for the system Ca_2+xNd_8?x(SiO₄)₆O_2?0.5x. The structures of two members of this system have been further refined from time-of-flight neutron powder diffraction data using the Rietveld method. Both structures belong to the $\text{P6}{}_3\text{m}$ space group and are isomorphous with natural apatite, Ca₁₀(PO₄)₆(F, OH)₂. Samples prepared at 1250°C exhibit an ordered distribution of Ca and Nd cations between two nonequivalent sites. The room temperature lattice parameters of Ca₂Nd₈(SiO₄)₆O₂ are a = 9.5291(5)Å and c = 7.0222(1) Å, while those of Ca_2.2Nd_7.8(SiO₄)₆O_1.9 are a = 9.5303(4) Å and c = 7.0147(1) Å. The composition of the latter member is believed to represent the upper limit of solid solution for this system at 1250°C.     

Rare-earth-substituted chloro-phosphate apatites

Compositions with the general formula Ln_xM_10?2xNa_x(PO₄)₆Cl₂ (Ln = Pr, Nd, Sm, Eu, Dy, Ho and Y; M = Ca, Sr, Ba, and Pb) have been prepared and studied by X-ray diffraction methods. The limited extent of rare earth substitution observed in chlorapatites in comparison to fluorapatites is attributed to the structural differences of the two systems.     

Excess molar enthalpies of {(1 − x2 − x3)Al + x2Bi + x3Ga}(I) alloys

The excess molar enthalpies H_m^E{(1 ? x₂ ? x₃)Al + x₂Bi + x₃Ga}(I) have been measured between 725 and 1170 K along the sections $\text{(1 ? x}{}_2\text{? x}{}_3\text{)}\text{x}{}_3\text{=}\text{1}\text{3}$, 1, and 3, and $\text{x}{}_2\text{x}{}_3\text{=}\text{1}\text{3}$, 1, and 3, with a high-temperature Calvet calorimeter using both the direct- and indirect-drop methods of mixing; experimental uncertainty is quoted respectively at 6.7 per cent and 9.9 per cent. The equilibrium temperatures confirmed phase boundaries previously determined by potentiometry, d.t.a., and calculation. Extrapolation of the experimental excess molar enthalpies to the limiting binary alloys {(1 ? x₂)Al + x₂Bi} allows new values for the excess molar enthalpies of these alloys to be proposed. The excess molar enthalpies of the ternary liquid mixtures can be represented correctly using these new values and Bonnier's equation.