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Energetic Effects of Substitution of La – Nd and Si – Ge Oxyapatite‐Type Materials
Author(s) -
Hosseini Seyedeh Mahboobeh,
Navrotsky Alexandra
Publication year - 2013
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.12705
Subject(s) - lanthanum , lanthanide , germanate , enthalpy , endothermic process , calorimetry , ionic radius , standard enthalpy of formation , inorganic chemistry , doping , materials science , neodymium , orthosilicate , oxide , silicate , chemistry , analytical chemistry (journal) , ion , thermodynamics , metallurgy , adsorption , nanotechnology , physics , optics , tetraethyl orthosilicate , chromatography , laser , optoelectronics , organic chemistry
A series of lanthanide oxyapatites, neodymium silicates ( Nd 9.33− x M 3 x /2 ( SiO 4 ) 6 O 2 ; x = 0.0 and 2.0 and M = Ca, Sr, and Ba), and lanthanum germanate ( La 10 ( GeO 4 ) 6 O 3 ) were prepared by a variety of heat treatments and characterized. High‐temperature oxide melt solution calorimetry in molten 2 PbO – B 2 O 3 solvent at 1078 K was performed to determine their enthalpies of formation from constituent oxides at room temperature. The energetics of these materials is discussed in terms of the effects of doping on two crystallographic sites, the lanthanide and tetrahedral sites. The enthalpy of formation from oxides becomes less exothermic by substituting La with Nd throughout the whole series, in both doped and undoped compositions, reflecting the smaller radius and lower basicity of Nd compared with La . Cation stoichiometric lanthanum germanate apatite ( La 10 ( GeO 4 ) 6 O 3 ) shows a more endothermic enthalpy of formation than the corresponding silicate, reflecting the larger radius and lower acidity of Ge than Si .