Al掺杂La10(SiO4)6O3的制备及其导电性能

以溶胶-凝胶法在850℃制备了Al掺杂La10(SiO4)6O3,即La10(SiO4)6-x(AlO4)xO3-0.5x(x=0,0.5,1.0,1.5和2.0),通过TG-DTA、XRD、IR和SEM表征,所得产品为磷灰石相。以电化学阻抗谱研究了其导电性能,发现决定电导率大小的因素有两种,一是间隙氧的数量,二是晶胞的大小,两种因素的综合作用,使得Al掺杂0.5时La10(SiO4)5.5(AlO4)0.5O2.75的电导率最大,在700℃时其电导率达到1.88×10-2S·cm-1。氧分压对电导率的研究表明,其主要的电荷载体是O2-离子。     

Silicate und Germanate mit der Struktur des Silicocarnotits

Silicates and Germanates with the Structure of Silicocarnotite A number of lanthanoid-containing compounds Ca₃Ln₂(XO₄)₃ with X = Si, Ge have been prepared, which have the silicocarnotite structure. With the silicates, Ln ranges from Sm to Lu, with the germanates only from Sm to Tb. Ca₃Y₂(SiO₄)₃ crystallizes in this structure type, too. In the case of Ln = La? Nd, mixtures “Ca₃Ln₂(XO₄)₃” are formed containing apatite phases. The germanates Ca₃Ln₂(GeO₄)₃ with Ln = Dy? Lu; Y, Sc and Ca₃Sc₂(SiO₄)₃ have the garnet structure, as already known. In addition, the lead compounds Pb₃La₂(SiO₄)₃, Pb₃Y₂(SiO₄)₃ and Pb₂Y₃(SiO₄)₃O_0,5 have been synthesized. They have an apatite structure where the halogen positions are unoccupied or half-occupied.     

The status of strontium in biological apatites: an XANES/EXAFS investigation

Osteoporosis represents a major public health problem through its association with fragility fractures. The public health burden of osteoporotic fractures will rise in future generations, due in part to an increase in life expectancy. Strontium‐based drugs have been shown to increase bone mass in postmenopausal osteoporosis patients and to reduce fracture risk but the molecular mechanisms of the action of these Sr‐based drugs are not totally elucidated. The local environment of Sr²⁺ cations in biological apatites present in pathological and physiological calcifications in patients without such Sr‐based drugs has been assessed. In this investigation, X‐ray absorption spectra have been collected for 17 pathological and physiological calcifications. These experimental data have been combined with a set of numerical simulations using the ab initioFEFF9 X‐ray spectroscopy program which takes into account possible distortion and Ca/Sr substitution in the environment of the Sr²⁺ cations. For selected samples, Fourier transforms of the EXAFS modulations have been performed. The complete set of experimental data collected on 17 samples indicates that there is no relationship between the nature of the calcification (physiological and pathological) and the adsorption mode of Sr²⁺ cations (simple adsorption or insertion). Such structural considerations have medical implications. Pathological and physiological calcifications correspond to two very different preparation procedures but are associated with the same localization of Sr²⁺versus apatite crystals. Based on this study, it seems that for supplementation of Sr at low concentration, Sr²⁺ cations will be localized into the apatite network.     

Darwin's Warm Little Pond: A One‐Pot Reaction for Prebiotic Phosphorylation and the Mobilization of Phosphate from Minerals in a Urea‐Based Solvent

The poor reactivity of insoluble phosphates, such as apatite‐group minerals, has been a long‐appreciated obstacle for proposed models of prebiotic organophosphate formation. This obstacle presents a significant challenge to the nascent development of an RNA world and other models for the origins of life on Earth. Herein, we demonstrate that a scenario based on the formation of a urea/ammonium formate/water (UAFW) eutectic solution leads to an increase in phosphorylation when compared to urea alone for phosphate sources of varying solubility. In addition, under evaporative conditions and in the presence of MgSO₄, the UAFW eutectic mobilizes the phosphate sequestered in water‐insoluble hydroxyapatite, giving rise to a marked increase in phosphorylation. These results suggest that the prebiotic concentrations of urea in a geologically plausible evaporitic environment could solve the problem of organic phosphorylation on a prebiotic Earth.     

Electroconductivity and transport numbers of solid electrolytes La10−x CaxA6O27−δ and La9.33+δA6−x AlxO26 (A = Si, Ge) with apatite-like structure

The ion-oxygen conductivity of apatite-like compounds based on lanthanum silicates and germanates La₁₀A₆O₂₇ (A = Si, Ge), La_10?x Ca_xSi₆O_27?δ (x = 0.25, 0.5, 1.0), La_9.75Ca_0.25Ge₆O_27?δ and La_9.33+δSi_6?x Al_xO₂₆(x=0.4, 0.8, 1.5) is studied in the interval of partial oxygen pressures pO₂ extending from 10^?16 to 10⁵ Pa, at temperatures of 500–1000°C. The electroconductivity of undoped compounds La₁₀A₆O₂₇ (A = Si, Ge) exceeds that of yttria-stabilized zirconia. The electroconductivity of lanthanum germanate (1.7 × 10^?2 and 8.5 × 10^?2S cm^?1 at 700 and 900°C, respectively) is substantially higher than that of lanthanum silicate (9.8 × 10^?3 and 3.5 × 10^?2 S cm^?1 at 700 and 900°C). Doping lanthanum germanate with calcium raises its electroconductivity (2.7 × 10^?2 and 1.3 × 10^?1 S cm^?1 for La_9.75Ca_0.25Ge₆O_27?δ at 700 and 900°C). Conversely, doping lanthanum silicate with ions of calcium or aluminum reduces the conductivity. In the pO₂ interval studied, the above compounds are ionic conductors and represent a class of solid electrolytes of promise for various electrochemical devices.     

ALa9(SiO4)6O2.5(A=Ca，Sr，Ba)的合成及其电性能

利用溶胶-凝胶法在850 ℃合成了硅酸盐氧基磷灰石ALa₉(SiO₄)₆O_2.5(A=Ca、Sr和Ba),经XRD表征所得产品为磷灰石相。以电化学阻抗谱研究了ALa₉(SiO₄)₆O_2.5的导电性能,发现A的原子半径越大,体系的电导率越高,活化能却减小。在700 ℃时BaLa₉(SiO₄)