Ca_9Fe(PO_4)_6(OH)_2的电子结构与形成能的第一性原理计算

基于第一性原理和热力学统计原理计算了单个Fe~(2+)替代羟基磷灰石晶胞中Ca~(2+)后晶体(Ca_9Fe(PO_4)_6(OH)_2)的电子结构和能够说明替代后结构稳定性的替位缺陷形成能.电子结构计算得出(Ca_9Fe(PO4)_6(OH)_2)的带隙值是1.85eV,而没有掺杂的是4.93e V,两者态密度特征相似,只是前者峰值变小了.理论形成能和溶液环境中的形成能的计算结果都表明Ca(B)更易被取代,但是两种形成能的值都大于0eV,具体是理论缺陷形成能的值都在7e V到8e V之间,溶液环境中的缺陷形成能主要和替代的位置、溶液的pH值以及Fe~(2+)在溶液中的浓度有关,且其值大于0eV,说明它们需要吸热才能发生替代,所以在羟基磷灰石中Fe~(2+)替代Ca~(2+)不容易发生.

First-principles study of electronic structure and defect formation energy of Ca9Fe(PO4)6(OH)2

The electronic structure and substitutional defect formation energy that elucidate thermodynamic stability of Ca₉Fe(PO₄)₆(OH)₂ which a divalent iron substitutes for calcium site in the unit cell of hydroxyapatite are calculated by first-principles and statistical theory of thermodynamics. The calculated band gap of the Ca₉Fe(PO₄)₆(OH)₂ is about 1.85eV, which is smaller than the 4.93eV( hydroxyapatite). And the feature of the total density of states of Ca₉Fe(PO₄)₆(OH)₂ is similar to that for hydroxyapatite, but the former peaks are lower than the latter. Computational results of theoretical defect formation energy and defect formation energy of solution show that the FeFe²⁺ ions prefer to substitute for Ca(B) sites, which is in agreement with the previous studies by Ming Jiang and Katsuyuki Matsunaga, but the value of the two kind of formation energy is bigger than zero, especially, theoretical formation energy is between 7eV and 8eV and defect formation energy of solution varies with the substitutional Ca sites, solution pH and the FeFe²⁺concentration, so all substitutions are energetically unfavorable because these substitutions are endothermic.