On the Study of Ca and Mg Deintercalation from Ternary Tantalum Nitrides
On the Study of Ca and Mg Deintercalation from Ternary Tantalum Nitrides
复制标题
三元氮化钽中Ca、Mg脱嵌的研究
作者：
R. Verrelli;A. Black;C. Frontera;J. Oró;M. E. Arroyo;A. Fuertes;M. R. Palacín
以二元氮化物Ta 3 N5和A3 N2（A：Mg，Ca）为原料，采用直接固相反应法制备了层状CaTaN 2和MgTa 2N 3以及立方相Mg 2 Ta 2N 4。CaTaN 2显示出轻微的Ca缺乏（每个分子式0.11摩尔），以及与先前报道的R3 π m对称性的单斜畸变，空间群C2/m，晶胞参数a = 5.4011（2），B = 3.1434（1），c = 5.9464（2）π，β = 107.91（3）°。研究了Ca ~（2+）和Mg ~（2+）在三种化合物中的脱嵌行为。对于MgTa 2N 3和Mg 2 Ta 2N 4，在与NO2 BF 4反应之后或在100 °C下在烷基碳酸酯电解质中电化学氧化之后，都不能推断出显著的Mg 2+提取。化学氧化Ca_（0.89）TaN_2的X射线粉末衍射图的Rietveld精修表明，Ca含量降低到0.34，同时单斜畸变消失，层间距从5.658扩展到5.762 μ m，空间群R3 μ m，晶胞参数a = 3.1103（1）和c = 17.287（1）μ m。该化合物的脱嵌也在100 °C下电化学实现。密度泛函理论计算的结果似乎表明，CaTaN 2氧化附加和/或替代脱嵌的反应机制正在发生，这可能与氧化后观察到的结晶度损失和过程的不可逆性有关。
Layered CaTaN2 and MgTa2N3 and cubic Mg2Ta2N4 were prepared by direct solid state reaction from the binary nitrides Ta3N5 and A3N2 (A: Mg, Ca). CaTaN2 showed a slight Ca deficiency (0.11 moles per formula), and a monoclinic distortion from previously reported R3̅m symmetry, with space group C2/m and cell parameters a = 5.4011(2), b = 3.1434(1), c = 5.9464(2) Å and β = 107.91(3)°. Ca2+ and Mg2+ deintercalation was investigated in the three compounds both chemically and electrochemically. No significant Mg2+ extraction could be inferred for MgTa2N3 and Mg2Ta2N4, neither after reaction with NO2BF4 nor after electrochemical oxidation at 100 °C in alkyl carbonate electrolytes. Rietveld refinement of the X-ray powder diffraction pattern of chemically oxidized Ca0.89TaN2 indicates a decrease of the Ca content to 0.34 concomitant to the disappearance of the monoclinic distortion and expansion of the interlayer space from 5.658 to 5.762 Å, space group R3̅m and cell parameters a = 3.1103(1) and c = 17.287(1) Å. Deintercalation in this compound was also achieved electrochemically at 100 °C. Results of density functional theory calculations seem to indicate that reaction mechanisms for CaTaN2 oxidation additional and/or alternative to deintercalation are taking place, which is likely related to the loss of crystallinity observed upon oxidation and the irreversibility of the process.