Hunold Oliver, Keuter Philipp, Bliem Pascal, Music Denis, Wittmers Friederike, Ravensburg Anna L, Primetzhofer Daniel, Schneider Jochen M
Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, D-52074 Aachen, Germany.
J Phys Condens Matter. 2017 Mar 1;29(8):085404. doi: 10.1088/1361-648X/aa5375. Epub 2017 Jan 12.
We have systematically studied the effect of transition metal valence electron concentration (VEC) of amorphous T YB (a-T YB, T = Sc, Ti, V, Y, Zr, Nb) on the elastic properties, bonding, density and electronic structure using ab initio molecular dynamics. As the transition metal VEC is increased in both periods, the bulk modulus increases linearly with molar- and mass density. This trend can be understood by a concomitant decrease in cohesive energy. T' = Ti and Zr were selected to validate the predicted data experimentally. A-TiYB and a-ZrYB thin films were synthesized by high power pulsed magnetron sputtering. Chemical composition analysis revealed the presence of up to 5 at.% impurities, with O being the largest fraction. The measured Young's modulus values for a-TiYB (301 ± 8 GPa) and a-ZrYB (306 ± 9 GPa) are more than 20% smaller than the predicted ones. The influence of O incorporation on the elastic properties for these selected systems was theoretically studied, exemplarily in a-TiYBO. Based on ab initio data, we suggest that a-TiYB exhibits a very dense B network, which is partly severed in a-TiYBO. Upon O incorporation, the average coordination number of B and the molar density decrease by 9% and 8%, respectively. Based on these data the more than 20% reduced Young's modulus obtained experimentally for films containing impurities compared to the calculated Young's modulus for a-TiYB (without incorporated oxygen) can be rationalized. The presence of oxygen impurities disrupts the strong B network causing a concomitant decrease in molar density and Young's modulus. Very good agreement between the measured and calculated Young's modulus values is obtained if the presence of impurities is considered in the calculations. The implications of these findings are that prediction efforts regarding the elastic properties of amorphous borides containing oxygen impurities on the at.% level are flawed without taking the presence of impurities into account.
我们利用从头算分子动力学系统地研究了非晶态T YB（a-T YB，T = Sc、Ti、V、Y、Zr、Nb）中过渡金属价电子浓度（VEC）对弹性性能、键合、密度和电子结构的影响。在这两个周期中，随着过渡金属VEC的增加，体模量随摩尔密度和质量密度呈线性增加。这种趋势可以通过内聚能的相应降低来理解。选择T' = Ti和Zr通过实验验证预测数据。通过高功率脉冲磁控溅射合成了a-TiYB和a-ZrYB薄膜。化学成分分析表明存在高达5 at.%的杂质，其中O的含量最高。测得的a-TiYB（301±8 GPa）和a-ZrYB（306±9 GPa）的杨氏模量值比预测值小20%以上。理论上研究了O掺入对这些选定体系弹性性能的影响，以a-TiYBO为例。基于从头算数据，我们认为a-TiYB呈现出非常致密的B网络，在a-TiYBO中部分被切断。掺入O后，B的平均配位数和摩尔密度分别降低了9%和8%。基于这些数据，与a-TiYB（未掺入氧）的计算杨氏模量相比，含杂质薄膜实验测得的杨氏模量降低20%以上是合理的。氧杂质的存在破坏了强B网络，导致摩尔密度和杨氏模量随之降低。如果在计算中考虑杂质的存在，则测得的和计算得到的杨氏模量值之间会有很好的一致性。这些发现的意义在于，如果不考虑杂质的存在，关于含氧量在at.%水平的非晶硼化物弹性性能的预测工作是有缺陷的。
