Solid solutions between β-Ca3(PO4)2 and sodium-containing whitlockite

Mixtures of CaHPO₄, CaCO₃, and Na₂CO₃ were heated at 870°C under steam or under dry CO₂ until phase composition and weight were constant. According to chemical analysis and X-ray diffractometry the stability field of the β-Ca₃(PO₄)₂ phase is limited by the molar P/Ca ratio of 0.664 ± 0.003 and 0.675 ± 0.010 irrespective of the partial water vapour pressure. A continuous series of solid solutions was found between β-Ca₃(PO₄)₂ and a new whitlockite with the composition Ca₁₀Na(PO₄)₇. The IR spectrum of these solid solutions shows that the point symmetry of the PO₄ groups and their environment increases with increasing sodium content. This is in agreement with data published about the structure of β-Ca₃(PO₄)₂ and whitlockite. The composition of these solid solutions suggests that Na⁺ ions can replace H⁺ ions in the whitlockite structure. Carbonate and pyrophosphate ions are not incorporated in these whitlockites.     

The Whitlockite Phase in the system CaO?P2O5?MgO at 1000°C

Mixtures of reagent grade CaHPO₄, MgO, and CaCO₃ were sintered at 1000°C both in air and in dry carbon dioxide to investigate the stability field of β-Ca₃(PO₄)₂ in the ternary CaO? P₂O₅? MgO system along the CaO? P₂O₅ and the β-Ca₃(PO₄)₂? Mg₃(PO₄)₂ join. The extent of substitution of Mg for Ca in β-Ca₃(PO₄)₂ was determined to be near 14.7% Mg of the cat-ions, both in air and in dry carbon dioxide. Lattice parameters of products with various degrees of substitution are presented. There is a decrease of the c-axis up to 10% substitution after which an increase of the c-axis occurs on further substitution of Ca by Mg. This is probably related to substitution in two different sublattices. At 1000°C the carbonate ion could not be incorporated in the β-Ca₃(PO₄)₂ structure, and along the CaO? P₂O₅ join the Ca/P range of solid solution for β-Ca₃(PO₄)₂ was found to be immeasurably small both in air and in dry carbon-dioxide.     

Synthesis and characterization of phosphates in molten systems Cs2O-P2O5-CaO-M2O3 (M—Al, Fe, Cr)

The crystallization of complex phosphates from the melts of Cs₂O-P₂O₅-CaO-M^III₂O₃ (M^III—Al, Fe, Cr) systems have been investigated at fixed value Cs/P molar ratios equal to 0.7, 1.0 and 1.3 and Са/Р=0.2 and Ca/М^III=1. The fields of crystallization of CsCaP₃O₉, β-Ca₂P₂O₇, Cs₂CaP₂O₇, Cs₃CaFe(P₂O₇)₂, Ca₉M^III(PO₄)₇ (M^III—Fe, Cr), Cs_0.63Ca_9.63Fe_0.37(PO₄)₇ and CsCa₁₀(PO₄)₇ were determined. Obtained phosphates were investigated using powder X-ray diffraction and FTIR spectroscopy. Novel whitlockite-related phases CsCa₁₀(PO₄)₇ and Cs_0.63Ca_9.63Fe_0.37(PO₄)₇ have been characterized by single crystal X-ray diffraction: space group R3c, a=10.5536(5) and 10.5221(4) Å, с=37.2283(19) and 37.2405(17) Å, respectively.     

Crystallographic studies of the role of Mg as a stabilizing impurity in β-Ca3(PO4)2. The crystal structure of pure β-Ca3(PO4)2

β-Ca₃(PO₄)₂ crystallizes in the rhombohedral space group R3c with unit cell parameters a = 10.439(1), c = 37.375(6) Å (hexagonal setting) and cell contents of 21 [Ca₃(PO₄)₂]. The structure was refined to R_w = 0.026, R = 0.030 using 1143 X-ray intensities collected from a single crystal by counter methods. Corrections were made for absorption, secondary extinction, and anomalous dispersion.The structure is related to that of Ba₃(VO₄)₂, but has lower symmetry because of the widely different ionic sizes of Ca and Ba. Seven [Ca₃(PO₄)₂] units occupy a volume corresponding to eight [Ba₃(PO₄)₂] units. The requirement of the c glide in β-Ca₃(PO₄)₂ has been shown in the least squares refinements to be attained by disorder of one cation over two sites. This disorder has a far-reaching effect on the structure.     

Beiträge zum thermischen Verhalten und zur Kristallchemie von wasserfreien Phosphaten XXXII [1] Neue Orthophosphate des zweiwertigen Chroms — Mg3Cr3(PO4)4, Mg3, 75Cr2, 25(PO4)4, Ca3Cr3(PO4)4 und Ca2, 00Cr4, 00(PO4)4

Contributions on Crystal Chemistry and Thermal Behaviour of Anhydrous Phosphates. XXXII. New Orthophosphates of Divalent Chromium — Mg₃Cr₃(PO₄)₄, Mg_{3, 75}Cr_{2, 25}(PO₄)₄, Ca₃Cr₃(PO₄)₄ and Ca_{2, 00}Cr_{4, 00}(PO₄)₄ Solid state reactions via the gas phase led in the systems A₃(PO₄)₂ / Cr₃(PO₄)₂ (A = Mg, Ca) to the four new compounds Mg₃Cr₃(PO₄)₄ ( A ), Mg_3.75Cr_2.25(PO₄)₄ ( B ), Ca₃Cr₃(PO₄)₄ ( C ), and Ca_2.00Cr_4.00(PO₄)₄ ( D ). These were characterized by single crystal structure investigations [( A ): P2₁/n, Z = 1, a = 4.863(2) Å, b = 9.507(4) Å, c = 6.439(2) Å, β = 91.13(6)°, 1855 independend reflections, 63 parameters, R1 = 0.035, wR2 = 0.083; ( B ): P2₁/a, Z = 2, a = 6.427(2) Å, b = 9.363(2) Å, c = 10.051(3) Å, β = 106.16(3)°, 1687 indep. refl., 121 param., R1 = 0.032, wR2 = 0.085; ( C ): P‐1, Z = 2, a = 8.961(1) Å, b = 8.994(1) Å, c = 9.881(1) Å, α = 104.96(2)°, β = 106.03(2)°, γ = 110.19(2)°, 2908 indep. refl., 235 param., R1 = 0.036, wR2 = 0.111; ( D ): C2/c, Z = 4, a = 17.511(2) Å, b = 4.9933(6) Å, c = 16.825(2) Å, β = 117.95(1)°, 1506 indep. refl., 121 param., R1 = 0.034, wR2 = 0.098]. The crystal structures contain divalent chromium on various crystallographic sites, each showing a (4+n)‐coordination (n = 1, 2, 3). For the magnesium compounds and Ca_2.00Cr_4.00(PO₄)₄ a disorder of the divalent cations Mg²⁺/Cr²⁺ or Ca²⁺/Cr²⁺ is observed. Mg_3.75Cr_2.25(PO₄)₄ adopts a new structure type, while Mg₃Cr₃(PO₄)₄ is isotypic to Mg₃(PO₄)₂. Ca₃Cr₃(PO₄)₄ and Ca_2.00Cr_4.00(PO₄) ₄ are structurally very closely related and belong to the Ca₃Cu₃(PO₄)₄‐structure family. The orthophosphate Ca₉Cr(PO₄)₇, containing trivalent chromium, has been obtained besides C and D .     

Mechanism of solid-state conversion of non-stoichiometric hydroxyapatite to diphase calcium phosphate

Two non-stoichiometric hydroxyapatites (n-HA) with Ca/P molar ratios of 1.50 and 1.58 and one stoichiometric hydroxyapatite (s-HA) with Ca/P = 1.67 were prepared from chemically pure CaHPO₄·2H₂O and KOH. After sintering at 1050 °C for 4 h, n-HA with Ca/P = 1.50 was transformed into -Ca₃(PO₄)₂, n-HA with Ca/P = 1.58 was converted to diphase calcium phosphate (DCP), while s-HA underwent no chemical transformations. The sintered and unsintered samples of hydroxyapatite were studied by IR spectroscopy, chemical analysis, and X-ray diffraction analysis. The crystallite dimensions were calculated, and a model for the DCP structure was proposed. The mechanism of the solid-state n-HA to DCP conversion was proposed on the basis of this model and published values of the volume diffusion coefficients of the OH^–, Ca²⁺, and PO₄ ^3– ions at 1000 °C.     

M5(PO4)3F (M=Ca, Sr, Ba)中Sm3+的电荷迁移态及Sm3+和Eu3+的电荷迁移能量关系

采用高温固相反应合成了M_5-2xSm_xNa_x(PO₄)₃F(M=Ca,Sr,Ba)荧光体,研究了其在真空紫外-可见光范围的发光特性。发现在Ca₅(PO₄)₃F中Sm³⁺的电荷迁移带约在191 nm,在Sr₅(PO₄)₃F中约在199 nm,而在Ba₅(PO₄)₃F中约在204 nm,随着被取代碱土离子半径的增大电荷迁移能量逐渐减小。比较了M₅(PO₄)₃F (M=Ca,Sr,Ba)中Sm³⁺和Eu³⁺电荷迁移能量的关系。     

The revised phase diagram of the Ca3(PO4)2–YPO4 system. The temperature and concentration range of solid-solution phase fields

A revised version of the Ca₃(PO₄)₂–YPO₄ phase diagram has been proposed on the basis of results obtained by thermal analysis (DTA/DSC/TG) and X-ray diffraction methods. A limited solid solution with the structure of β-Ca₃(PO₄)₂ exists in the system. At 1,100 °C the maximal concentration of YPO₄ in the solid solution is ~15 mass%. The solid-solution phase field exists in the temperature range upto ~1,380 °C. Two high-temperature solid solutions with the structure of α′ and α-Ca₃(PO₄)₂ form in system as well, however only the α phase can be obtained by quenching from high temperatures. The Ca₃Y(PO₄)₃ compound with the structure of eulytite forms in the Ca₃(PO₄)₂–YPO₄ system at temperatures exceeding 1,255 °C and does not show any polymorphic transition.     

Phase equilibria in the tricalcium phosphate-mixed calcium sodium (potassium) phosphate systems

Phase equilibria in the quasi-binary sections Ca₃(PO₄)₂-CaMPO₄ (M = Na, K) are distinguished by high-temperature isomorphism of glaserite-like phases α’-Ca₃(PO₄)₂ and α-CaMPO₄. The main differences of the Ca₃(PO₄)₂-CaKPO₄ system from the Ca₃(PO₄)₂-CaNaPO₄ system are a shift of invariant equilibria toward higher temperatures, deceleration of phase transformations, and the emergence of polymorphism of an intermediate phase of an ordered solid solution based on α-CaKPO₄. The low-temperature modification of this phase of a composition near Ca₈K₂(PO₄)₆ has the apatite structure with unoccupied hexagonal channels.     

Thermodynamics Analysis and Removal of P in a P-(M)-H2O System

In order to efficiently remove phosphorus, thermodynamic equilibrium diagrams of the P-H₂O system and P-M-H₂O system (M stands for Fe, Al, Ca, Mg) were analyzed by software from Visual MINTEQ to identify the existence of phosphorus ions and metal ions as pH ranged from 1 to 14. The results showed that the phosphorus ions existed in the form of H₃PO₄, H₂PO₄⁻, HPO₄²⁻, and PO₄³⁻. Among them, H₂PO₄⁻ and HPO₄²⁻ were the main species in the acidic medium (99% at pH = 5) and alkaline medium (97.9% at pH = 10). In the P-Fe-H₂O system ((P) = 0.01 mol/L, (Fe³⁺) = 0.01 mol/L), H₂PO₄⁻ was transformed to FeHPO₄⁺ at pH = 0–7 due to the existence of Fe³⁺ and then transformed to HPO₄²⁻ at pH > 6 as the Fe³⁺ was mostly precipitated. In the P-Ca-H₂O system ((P) = 0.01 mol/L, (Ca²⁺) = 0.015 mol/L), the main species in the acidic medium was CaH₂PO₄⁺ and HPO₄²⁻, and then transformed to CaPO₄⁻ at pH > 7. In the P-Mg-H₂O system ((P) = 0.01 mol/L, (Mg²⁺) = 0.015 mol/L), the main species in the acidic medium was H₂PO₄⁻ and then transformed to MgHPO₄ at pH = 5–10, and finally transformed to MgPO₄⁻ as pH increased. The verification experiments (precipitation experiments) with single metal ions confirmed that the theoretical analysis could be used to guide the actual experiments.     

Calcium phosphate powders synthesized from solutions with [Ca2+]/[PO 4 3− ]=1 for bioresorbable ceramics

Calcium phosphate powders for manufacturing bioceramics were synthesized via precipitation from stock solutions of (NH₄)₂HPO₄ and Ca(NO₃)₂, or CaCl₂ or Ca(CH₃COO)₂ with [Ca²⁺]/[PO₄³⁻] = 1, without pH regulation. Properties of powdered samples, including density and microstructure of ceramics sintered at 900, 1000, 1100°C, were studied. The following pairs of precursors such as Ca(NO₃)₂/(NH₄)₂HPO₄, CaCl₂/(NH₄)₂HPO₄, Ca(CH₃COO)₂/(NH₄)₂HPO₄ gave both insoluble calcium phosphates and the corresponding by-products of synthesis — NH₄NO₃, NH₄Cl, NH₄CH₃COO. These by-products were released from the calcium phosphate precipitates in the course of heating to the temperature of sintering. Owing to specific buffer properties of the solutions being formed during synthesis, the pH value varied in a wide range during the precipitation process leading to different final values of pH and, thus, to different target phase(s) after annealing at 900–1100°C. After sintering, the samples based on the powders synthesized from Ca(NO₃)₂/(NH₄)₂HPO₄ consisted of β-Ca₂P₂O₇, whereas the samples based on the powders derived from CaCl₂/(NH₄)₂HPO₄ were composed of β-Ca₂P₂O₇ and β-Ca₃(PO₄)₂, and the samples based on the powders synthesized from Ca(CH₃COO)₂/(NH₄)₂HPO₄ contained only β-Ca₃(PO₄)₂. All the powders can be considered as the precursors for fabrication of bioceramics with enhanced resorption.      

Kristallographische Orientierungsbeziehungen zwischen den Phasen der Reaktionsfolge Ca2[P4O12] · 4 H2O → β-(Ca2[PO3]4)x

Crystallographic Orientation Relations between the Phases in the Reaction Ca₂[P₄O₁₂] · 4 H₂O → β-(Ca₂[PO₃]₄)_x The dehydration of Ca₂[P₄O₁₂] · 4 H₂O modification I proceeds over several intermediate phases to β-(Ca₂[PO₃]₄)_x crystallographically oriented. One of the intermediate phases is X-ray amorphous. It is of special interest, that this amorphous phase does not interrupt the oriented course of the reaction. The β-polyphosphate transforms to β-Ca₂[P₂O₇] connected with the loss of P₂O₅ at further heating. The crystallographic orientation relations between educt and product were determined for all steps of the reaction. The unit cells of the phases were determined too.     

On Aliovalent Substitution on the Li Site in LiMPO4: an ­X‐ray Diffraction Study of the Systems LiMPO4–M1.5PO4 (= LixM1.5–x/2PO4; M = Ni,Co, Fe,Mn)

In this paper we report on the possibility of Li substitution by M²⁺ to various high degrees in LiMPO₄ olivine‐type compounds (M = Ni, Co, Fe, Mn), depending on the kind of transition metal M. The experimental studies were carried through by reacting stoichiometric amounts of LiM^IIPO₄ and M^II_1.5PO₄ (= M^II₃(PO₄)₂) to form compounds of composition Li_xM^II_1.5–x/2PO₄ (0 ≤ x ≤ 1). A complete solid solution over the whole range of x was found for M = Ni (together with a second order structural transition from orthorhombic to monoclinic for decreasing x), whereas far smaller degrees of dopability of the Li site were found for LiCoPO₄ and LiFePO₄ (up to compositions of approx. (Li_0.8Co_0.1)CoPO₄ and approx. (Li_0.9Fe_0.05)FeO₄. In addition, the nearly stoichiometric monoclinically distorted olivine‐type compounds with compositions (Li_0.42–0.47Co_0.29–0.265)CoPO₄ and (Li_0.14–0.16Fe_0.43–0.42)FePO₄ could be identified and are described in this article.     

Characterization of sol-gel processing of calcium phosphate thin films on silicon substrate by FTIR spectroscopy

Calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, CHAp) films were obtained on silicon substrates by a sol-gel method using a spin-coating technique. In the sol-gel process, ethylendiamintetraacetic acid and 1,2-ethandiol, triethanolamine and polyvinyl alcohol were used as complexing agents and gel network forming agents, respectively. The samples were annealed at 1000 °C for 5 h in air after each spinning procedure. Spin-coating and annealing procedures were repeated 5, 8 and 10 times. The coatings were characterized using X-ray diffraction (XRD), scanning electron microscopy- energy dispersive X-ray spectroscopy (SEM-EDX) and Fourier Transform infrared spectroscopy (FTIR). FTIR-spectroscopy allowed us to predict the formation of oxyhydroxyapatite Ca₁₀(PO₄)₆(OH)_2-2xO_x on the Si substrate. Moreover, according to the FTIR results, the side phase β-Ca₃(PO₄)₂ has been formed instead of α-Ca₃(PO₄)₂. In addition, the anhydrous dicalcium, phosphate phase CaHPO₄ was also detected spectroscopically.     

Synthesis and phase formation in M 0.5(1+x) 2+ FexTi2−x (PO4)3 phosphate series

New complex phosphates of titanium, iron, and alkaline-earth metals have been synthesized. X-ray powder diffraction, differential thermal analysis (DTA), and IR spectroscopy are used to study phase formation in the series of M_0.5(1+x)Fe_xTi_2?x (PO₄)₃ (M = Mg, Ca, Sr, Ba) phosphates. Individual compounds and solid solutions are found to crystallize in the NaZr₂(PO₄)₃ and K₂Mg₂(SO₄)₃ structure types. Their crystal parameters are calculated. CaFeTi(PO₄)₃ is studied using Mössbauer spectroscopy. Its structure is refined by the Rietveld method: space group $R\bar 3$ c, Z = 6, a = 8.5172(1), Å, c = 21.7739(4) Å, V = 1367.91(4) ų.     

A Partial System LaPO4-Ca2P2O7-Ca(PO3)2-La(PO3)3

The system LaPO₄-Ca₂P₂O₇-Ca(PO₃)₂-La(PO₃)₃ was investigated by means of thermal and X-ray analyses. Three binary systems were found to occur in this region: LaPO₄-Ca(PO₃)₂,LaPO₄-Ca₄P₆O₁₉ and LaPO₄-CaLa(PO₃)₅. Their phase diagrams, and also that for the system LaPO₄-Ca₂P₂O₇- Ca(PO₃)₂-La(PO₃)₃, were obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fe6.67(PO4)5.35(HPO4)0.65 and Fe6.23(PO4)4.45(HPO4)1.55: two new mixed‐valence iron phosphates

Two new mixed‐valence iron phosphates, namely heptairon pentaphosphate hydrogen phosphate, Fe_6.67(PO₄)_5.35(HPO₄)_0.65, and heptairon tetraphosphate bis(hydrogen phosphate), Fe_6.23(PO₄)_4.45(HPO₄)_1.55, have been synthesized hydrothermally at 973 K and 0.1 GPa. The structures are similar to that of Fe^II₃Fe^III₄(PO₄)₆ and are characterized by infinite chains of Fe polyhedra parallel to the [101] direction. These chains are formed by the Fe1O₆ and Fe2O₆ octahedra, alternating with the Fe4O₅ distorted pentagonal bipyramids, according to the stacking sequence ...Fe1–Fe1–Fe4–Fe2–Fe2.... The Fe3O₆ octahedra and PO₄ tetrahedra connect the chains together. Fe^II is localized on the Fe3 and Fe4 sites, whereas Fe^III is found in the Fe1 and Fe2 sites, according to bond‐valence calculations. Refined site occupancies indicate the presence of vacancies on the Fe4 site, explained by the substitution mechanism Fe^II + 2(PO₄³⁻) = vacancies + 2(HPO₄²⁻).     

Dissolution De L'hydroxyapatite et Du Phosphate Tricalcique β Dans Les Solutions D'acide Nitrique

Using an isoperibol calorimeter for rapid reactions and a Calsol type microcalorimeter for slow processes, are applied to determine the enthalpies of solution of two synthetic phosphate products in nitric acid. Namely, β tricalcium phosphate Ca₃(PO₄)₂ and the calcium hydroxyapatite Ca₁₀ (PO₄)₆ (OH)₂ are measured by varying pH value of the solvent. Some dissolution mechanisms are proposed for various pH values. They are ensured by complementary reactions of solution of Ca(NO₃)₂, Ca(H₂ PO₄)₂ and H₃ PO₄ in the same solvents. An extrapolation of solution enthalpies to pH=7 leads to the enthalpy of solution of these products in the pure water. These values are Δ_sol H °=–138.3 kJ mol^–1 for Ca₃ (PO₄)₂ and –393.6 kJ mol^–1 for Ca₁₀ (PO₄)₆ (OH)₂ . This revised version was published online in August 2006 with corrections to the Cover Date.     

Eu luminescence—a structural probe in BiCa4(PO4)3O, an apatite related phosphate

Eu³⁺ luminescence is studied in apatite-related phosphate BiCa₄(PO₄)₃O. Compositions of the formula Bi_1−xEu_xCa₄(PO₄)₃O [x=0.05, 0.1, 0.3, 0.5, 0.8 and 1.0] are synthesized and they are isostructural with parent BiCa₄(PO₄)₃O. Room temperature photoluminescence shows the various transitions ⁵D₀→⁷F_J(=0,1,2) of Eu³⁺. The emission results of compositions with different Eu³⁺ content show the difference in site occupancy of Eu³⁺ in Bi_1−xEu_xCa₄(PO₄)₃O. The intense ⁵D₀-⁷F₀ line at 574 nm for higher Eu³⁺ content is attributed to the presence of strongly covalent Eu-O bond that is possible by substituting Bi³⁺ in the Ca(2) site. This shows the preferential occupancy of Bi³⁺ in Ca(2) site and this has been attributed to the 6s² lone pair electrons of Bi³⁺. This is further confirmed by comparing the emission results with La_0.95Eu_0.05Ca₄(PO₄)₃O.     

MGe(PO4)2 (M=Ca, Sr, Ba): Crystal structure, phase transitions and thermal expansion

Three earth alkali-germanium monophosphates M^IIGe(PO₄)₂ (M=Ca, Sr, Ba) were prepared by solid state reaction and their structures, previously unknown, studied by Rietveld analysis. BaGe(PO₄)₂ and high-temperature β-SrGe(PO₄)₂ (space group C2/m, Z=2) are fully isotypic with yavapaiite, whereas CaGe(PO₄)₂ and low-temperature α-SrGe(PO₄)₂ (C2/c, Z=4) are distorted derivatives. The phase transition between the two forms is observed for the first time. The thermal expansion, resulting from several structural mechanisms, is very anisotropic.