Phase and melting relationships of β, α and α′-Ca3(PO4)2 polymorphs in the Ca3(PO4)2-Zn3(PO4)2 system

In order to provide an exact knowledge of the phase transitions and melting relationships of Ca₃(PO₄)₂ (TCP) in the presence of zinc, a revisited version of the rich-Ca₃(PO₄)₂ region of the phase diagram of the system Ca₃(PO₄)₂-Zn₃(PO₄)₂ has been established in the present work. Experimental determination of this diagram was carried out by solid-state reactions of samples prepared from pure NH₄H₂PO₄, CaCO₃ and ZnO raw materials. X-ray Diffraction, Differential Thermal Analyses and Field Emission Scanning Electron Microscopy studies allowed to revise the α, β, α + β-TCP phase stability fields, delimitating for the first time the biphasic α + α′-TCP field and the melting relationships in the high temperature region of the system. The results allowed to determine two peritectic invariant points, at ≈1400 °C for 95 mol% Ca₃(PO₄)₂ and at ≈1490 °C for ≈99.5 mol% Ca₃(PO₄)₂.     

Synthesis,structure and characterization of (NH4)2[Cu2(H2O)4(NH3CH2COO)2(NH2CH2COO)2]H2V10O28·6H2O

The decavanadate with a novel glycine–glycinato complex of copper (II) in the cationic part, (NH₄)₂[Cu₂(H₂O)₄(NH₃CH₂COO)₂(NH₂CH₂COO)₂]H₂V₁₀O₂₈·6H₂O (1), has been prepared and characterized by elemental analysis, infrared and EPR spectroscopies. The triplet X band EPR spectrum of powdered sample evidenced magnetic interaction between the Cu(II) atoms in the dimeric unit which is probably realized through the bridging water molecules in this part of the complex. A single crystal X-ray diffraction study revealed that the structure of 1 contains cationic copper complex with a rare Cu(H₂O)₂Cu double bridge. In this cation, a simultaneous bidentate N, O– and monodentate O– coordination of glycine to the same central atom was observed for the first time.     

Crystal Structure and Physicochemical Properties of Two Supramolecular Compounds: (C4H8NH2)4[Mo8O26] and (NH4)Na2[AsIIIMo6O21(O2CCH2NH3)3]·8H2O

Two inorganic–organic hybrid supramolecular compounds based on polyoxometalates formulated as (C₄H₈NH₂)₄[Mo₈O₂₆] (1) and (NH₄)Na₂[As^IIIMo₆O₂₁(O₂CCH₂NH₃)₃]·8H₂O (2) have been synthesized by conventional solution method and characterized by infrared, UV–Vis and single-crystal X-ray diffraction analyses. Thermal analysis was performed to study their thermal stability. The atomic arrangement in compound (1) can be described as inorganic layers built by [Mo₈O₂₆]^4?, pyrrolidinium cations are embedded into layers. The fascinating structural feature of compound (2) is that the glycine molecules are bounded to two edge-sharing Mo centers via their carboxylate functionality leading to functionalized heteropolymolybdate [As^IIIMo₆O₂₁(O₂CCH₂NH₃)₃]^3?, extensive net hydrogen bonds between cations and anions contribute to the crystal packing. The electrochemical behavior of compound (2) has been studied.     

NZP族磷酸盐晶体化合物NH4Zr2(PO4)3的水热合成

以(NH4)2HPO4为磷源,ZrO(NO3)2为锆源,用共沉淀法合成无定形前驱体,进一步采用水热晶化法制备出了NH4Zr2(PO4)3结晶化合物.研究了晶种、矿化剂(氟离子)添加量、水热合成温度和时间、pH值等对形成具有NaZr2P3O12(NZP)族晶体结构的化合物的影响,得到的最温和的水热晶化合成条件,即:按摩尔比n(F-)/n(ZrO2=1 HF引入HF作为矿化剂,添加占产物质量15%的晶种,在pH=1～5的酸性环境下,在50℃水热合成24h,可以得到结晶良好的单相NH4Zr2(PO4)3,用Brunauer-Emmett-Teller氮吸附法测定其比表面积为3.17m2/g,总孔容为0.00493mL/g.结果表明:所合成的具有三维网络状骨架结构的NZP族结晶化合物NH4Zr2(PO4)3因不具备类似微孔沸石分子筛的多孔性质,故更适合作为NZP族陶瓷的粉体材料而非分子筛催化材料.     

Microstructure–conductivity relationship of Na3Zr2(SiO4)2(PO4) ceramics

The ionic conductivity of solid electrolytes is dependent on synthesis and processing conditions, ie, powder properties, shaping parameters, sintering time (t_s), and sintering temperature (T_s). In this study, Na₃Zr₂(SiO₄)₂(PO₄) was sintered at 1200 and 1250°C for 0-10 hours and its microstructure and electrical performance were investigated by means of scanning electron microscopy and impedance spectroscopy. After sintering under all conditions, the sodium super-ionic conductor-type structure was formed along with ZrO₂ as a secondary phase. The microstructure investigation revealed a bimodal particle size distribution and grain growth at both T_s. The density of samples increased from 60% at 1200°C for 0 hours to 93% at 1250°C for 10 hours. The ionic conductivity of the samples increased with t_s due to densification and grain growth, ranging from 0.13 to 0.71 mS/cm, respectively. The corresponding equivalent circuit fitting for the impedance spectra revealed that grain boundary resistance is the prime factor contributing to the changing conductivity after sintering. The activation energy of the bulk conductivity (E_a,bulk) remained almost constant (0.26 eV) whereas the activation energy of the total conductivity (E_a) exhibited a decreasing trend from 0.37 to 0.30 eV for the samples with t_s = 0 and 10 hours, respectively—both sintered at 1250°C. In this study, the control of the grain boundaries improved the electrical conductivity by a factor of 6.     

A Novel Mixed-Valence Tetranuclear Iron-Oxygen Clusters in the Organically Templated Iron Phosphate [H3N(CH2)2NH3]2 Fe4O(PO4)4 ċH2O

A novel iron phosphate templated with ethylenediammonium cation, [H₃N(CH₂)₂NH₃]₂ Fe₄ O(PO₄)₄H₂O, has been synthesized hydrothermally and characterized by single-crystal X-ray diffraction, thermo-gravimetric analysis, magnetic susceptibility and Mossbauer spectroscopy. The compound crystallizes in the mono-clinic space group C2 with a= 30.3801(5),b= 10.1204(5),c= 10.0977(5) Å, = 107.712(1)°, V = 2957.5(4) ų and Z = 6. The structure contains 5 and 6-coordinated Fe atoms bridged by ₄-oxygen and PO₄ groups to form two types of mixed-valence Fe₄P₄ cubane-like clusters, which are connected via Fe- O- P bonds to give rise to intersecting channels that house the ethylenediammonium cations and water molecules. Room-temperature Mossbauer data confirm the presence of Fe^II and Fe^III.     

Suppressing fire hazard of poly(vinyl alcohol) based on (NH4)2[VO(HPO4)]2(C2O4)·5H2O with layered structure

Two-dimensional layered ammonium vanadium oxalate-phosphates (AVOPh) with the structural formula of (NH₄)₂[VO(HPO₄)]₂(C₂O₄)·5H₂O are synthesized though a hydro-thermal method, which is dispersed into poly(vinyl alcohol) (PVA) matrix to prepare PVA/AVOPh composites. The results of thermal analysis indicate that AVOPh and PVA have similar decomposition temperature from 280 to 500°C, which is critical for choosing flame retardant. The incorporation of AVOPh significantly improves the thermal stability and flame retardancy of PVA/AVOPh composites that the T_5% value of PVA/2 wt% AVOPh composites is up to 215°C, and the residue of PVA/8 wt% AVOPh composites is enhanced to 16.9%, while those of pure PVA are only 178°C and 2.4%. PVA/4 wt% AVOPh composites can pass V-0 level, and its limiting oxygen index value is up to 32.0%. Furthermore, the peak heat release rate (PHRR) and total heat release (THR) of PVA/AVOPh composites are obviously decreased, which reduced by 43.4% and 43.8% with the addition of 4 wt% AVOPh, compared with those of pure PVA. The excellent thermal stability and flame retardancy are mainly attributed to the uniform dispersion and barrier effect of 2D layered AVOPh, the release of crystal water, ammonia and phosphorus free radicals and the two-phase flame retardant catalytic mechanism of vanadium and phosphorus.     

KH2PO4-KCl-H2O、NH4H2PO4-NH4Cl-H2O三元体系283.15 K相平衡研究

采用等温溶解平衡法研究了三元体系KH₂PO₄-KCl-H₂O、NH₄H₂PO₄-NH₄Cl-H₂O在283.15 K时的相平衡,并用湿渣法与X射线衍射相结合的方法鉴定了平衡固相的组成与结构。结果表明,三元体系KH₂PO₄-KCl-H₂O和NH₄H₂PO₄-NH₄Cl-H₂O为简单共饱和型,无固溶体或加合物形成,每个相图包含1个不变点、2条单变量曲线和3个结晶区。运用Pitzer电解质溶液理论计算了简单三元体系KH₂PO₄-KCl-H₂O、NH₄H₂PO₄-NH₄Cl-H₂O的饱和溶解度数据,结果表明,KH₂PO₄-KCl-H₂O体系的相对平均偏差为0.046,均方根偏差为0.29,NH₄H₂PO₄-NH₄Cl-H₂O体系的相对平均偏差为0.044,均方根偏差为0.31,溶解度理论计算结果与实验值基本一致。     

Facile fabrication of NH(4)CoPO(4)·H(2)O nano/microstructures and their primarily application as electrochemical supercapacitor

Various NH(4)CoPO(4)·H(2)O nano/microstructures (oblong plate, microplate, microflower, hierarchical architectures) have been synthesized through a facile chemical precipitation method without surfactants and templates. More importantly, the supercapacitive performances of NH(4)CoPO(4)·H(2)O nano/microstructures were firstly studied using cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy methods in 3.0 M KOH solution. These results indicated that NH(4)CoPO(4)·H(2)O hierarchical architectures electrodes exhibit effective supercapacitive characteristics in aqueous KOH electrolyte. The specific capacitance of NH(4)CoPO(4)·H(2)O electrode is up to 369.4 F g(-1) at a current density of 0.625 A g(-1) and the material has a long cycle life which can maintain 99.7% of initial specific capacitance after 400 cycles.     

25℃下K2SO4-(NH4)2SO4-CO(NH2)2-H2O四元体系的相平衡

测定了25℃下K2SO4-CO(NH2)2-H2O及(NH4)2SO4-CO(NH2)2-H2O两个三元体系相平衡的数据，并依据Pitzer电解质溶液理论对实验测定值进行了关联，关联结果与实验测定值相吻合．通过测定25℃下K2SO4-(NH4)2SO4-CO(NH2)2-H2O四元体系的相平衡数据可知尿素不能与硫酸钾或硫酸铵形成复盐，因此该四元体系的相平衡数据可近似由其所含三元体系的相互作用参数推算得出．     

Tunable photoluminescence of apatite phosphor Ca5.95−xSrxLa4(SiO4)2(PO4)4O2:0.05Eu2+ and its application in light-emitting diodes

A series of new apatite phosphors Ca_5.95−xSr_xLa₄(SiO₄)₂(PO₄)₄O₂:0.05Eu²⁺ (x = 0-5.95) were prepared with the solid-state method. The variations of the occupation rate and cell parameters were investigated in detail, demonstrating that the phosphors are pure phases and that the different occupation rates of La³⁺, Ca²⁺, and Sr²⁺ ions are due to the different electrostatic bond strengths. The reflectance and photoluminescence excitation spectra prove that the phosphors can be efficiently excited with near-ultraviolet (n-UV) light. The broad redshift (50 nm) in the photoluminescence spectra is attributed to the increase in the crystal field splitting when the Ca²⁺ ion is replaced by the larger Sr²⁺ ion. At 150°C, the obtained phosphors maintain an emission intensity of ~67%-77% of that at room temperature (25°C), which indicates relatively the high performance of apatite phosphors in the temperature-dependence experiment. Because of the substitution of the small Ca²⁺ ion by the large Sr²⁺ ion, the emission color changes from green to yellow. Finally, a series of self-made light emitting diodes lamps were fabricated by coating the Ca_5.95−xSr_xLa₄(SiO₄)₂(PO₄)₄O₂:0.05Eu²⁺ phosphors with commercial blue and red phosphors on an n-UV chip (λ_ex = 370 nm). The self-made white-emitting lamps display a continuous changing correlated color temperature (4053-9353 K) or commission international de L'eclairgae (from [0.29, 0.28] to [0.38, 0.37]), implying that the series apatite phosphors have great potential to meet the different requirements of applications.     

Structure and physical properties of Ba(PO3)2–AlF3–BaSO4 fluoro-sulfo-phosphate glasses

Alkali-earth-metaphosphate-based fluoro-sulfo-phosphate M(PO₃)₂–AlF₃–MSO₄ (MPFS, M = Ca, Sr, Ba) glasses have been developed via simultaneously incorporating fluoride and sulfate into metaphosphate glass. Their glass-forming regions were efficiently determined under the guidance of thermodynamic calculation method. The physical and structural properties of BaPFS glass were investigated in detail. Furthermore, near-infrared spectroscopic properties of Er³⁺-doped BaPFS (Er–BaPFS) glass were studied. Physical parameters, such as Abbe's number ν_d (55-75) and nonlinear refractive index n₂ (1.17-1.86 × 10⁻¹³ esu), of BaPFS glass are strongly depended on P/F/S ratio. The structure of BaPFS glass gradually depolymerizes and tends to become multianionic when Ba(PO₃)₂ is substituted by AlF₃ and BaSO₄. Anion-substitution strategy effectively modulates the property and structure of glass, providing a scheme to derive glass materials. In addition, enhanced emission at ~1.5 μm has been observed from Er–BaPFS glass along with large emission cross section (5.0-5.5 × 10⁻²¹ cm²) and long lifetime (6.7-7.3 ms), resulting in large figure of merit (3.46-3.84 × 10⁻²³ cm²·s), which is a promising candidate for solid-state laser.     

Influence of vanadium substitution on sintering behaviour of Pb3(VO4)2(1−x)(PO4)2x ceramics

Intermediate-stage sintering has been investigated in lead orthophosphovanadates Pb₃(VO₄)_2(1−x)(PO₄)_2x. It was found that rich-vanadium compounds such as Pb₃(VO₄)₂ and Pb₃(VO₄)_1.6(PO₄)_0.4 densify rapidly with important grain growth. For these compounds grain growth is controlled by grain boundaries and densification occurs by a mixed mechanism with lattice and grain boundary diffusion. For Pb₃(PO₄)₂, sintering mechanism supports a model of grain-boundary-controlled densification and grain growth is a surface diffusion-controlled pore drag mechanism. Moreover, the presence of phosphorus in compounds' formulae, tends to decrease the grain-boundary mobility, preventing pore-boundary separation. The kinetics analysis highlights the importance of vanadium substitution in modifying the diffusion coefficient of rate-limiting species.     

25℃下K2SO4–(NH4)2SO4–CO(NH2)2–H2O四元体系的相平衡

测定了25℃下K2SO4–CO(NH2)2–H2O及(NH4)2SO4–CO(NH2)2–H2O 两个三元体系相平衡的数据，并依据Pitzer电解质溶液理论对实验测定值进行了关联，关联结果与实验测定值相吻合. 通过测定25℃下K2SO4–(NH4)2SO4–CO(NH2)2–H2O四元体系的相平衡数据可知尿素不能与硫酸钾或硫酸铵形成复盐，因此该四元体系的相平衡数据可近似由其所含三元体系的相互作用参数推算得出.     

Oxidative dehydrogenation of ethane and propane over magnesium–cobalt phosphates CoxMg3−x(PO4)2

The magnesium–cobalt phosphates Co_xMg_3–x(PO₄)₂ belonging to the olivine-type structure were synthesized by coprecipitation and then investigated in the oxidative dehydrogenation (ODH) of ethane and propane. The best yields, with the exception of Co_0.5Mg_2.5(PO₄)₂, were achieved with the compositions ranging between 1x2.5. Magnesium phosphate Mg₃(PO₄)₂ displayed no activity and pure cobalt phosphate Co₃(PO₄)₂ was found to be the less active component of the solid solution. Comparison of the catalysts performances showed that they all have similar activity in ethane and propane ODH, albeit, they are more selective in propylene than in ethylene production. The Co_xMg_3–x(PO₄)₂ solid solution was also studied, for characterization purposes, in butan-2-ol conversion. The samples presented acid–base properties due essentially to the (PO–H) groups but they do not bear conventional redox centers. All the catalysts were active at low temperatures in the alcohol dehydration. The dehydrogenation activity versus the phosphates composition displayed two maxima around x=1 and 2, respectively. Similar striking behavior was also observed in ethane and propane ODH. UV-visible investigations of Co_xMg_3–x(PO₄)₂ showed, in agreement with the XRD data, that the Co^{2 +} ions are distributed in the phosphate framework between six- and five-coordinated sites. The cobalt atoms in the five-coordinated sites Co(5) and their Co(5)–Co(5) interatomic distances were assumed to play the main role in the C–H bond activation and the appearance of maxima in the activity. Magnesium cations presumably intervene in acid–base properties of the samples and O₂ activation. Characterization of the samples showed that they do not undergo any noticeable transformation after the catalytic tests.