Beltrán A, Andrés J, Sambrano J R, Longo E
Departament de Química Física i Analítica, Universitat Jaume I, Campus de Riu Sec, Castelló E-12071, Spain.
J Phys Chem A. 2008 Sep 25;112(38):8943-52. doi: 10.1021/jp801604n. Epub 2008 Aug 5.
The present study is concerned with the structural and electronic properties of the TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 composite systems. Periodic quantum mechanical method with density functional theory at the B3LYP level has been carried out. Relaxed surface energies, structural characteristics and electronic properties of the (110), (010), (101) and (00) low-index rutile surfaces for TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 models are studied. For comparison purposes, the bare rutile TiO2 and SnO2 structures are also analyzed and compared with previous theoretical and experimental data. The calculated surface energy for both rutile TiO2 and SnO2 surfaces follows the sequence (110) < (010) < (101) < (001) and the energy increases as (010) < (101) < (110) < (001) and (010) approximately = (110) < (101) < (001) for SnO2/TiO2/SnO2 and TiO2/SnO2/TiO2 composite systems, respectively. SnO2/TiO2/SnO2 presents larger values of surface energy than the individual SnO2 and TiO2 metal oxides and the TiO2/SnO2/TiO2 system renders surface energy values of the same order that the TiO2 and lower than the SnO2. An analysis of the electronic structure of the TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 systems shows that the main characteristics of the upper part of the valence bands for all the studied surfaces are dominated by the external layers, i.e., by the TiO2 and the SnO2, respectively, and the topology of the lower part of the conduction bands looks like the core layers. There is an energy stabilization of both valence band top and conduction band bottom for (110) and (010) surfaces of the SnO2/TiO2/SnO2 composite system in relation to their core TiO2, whereas an opposite trend is found for the same surfaces of the TiO2/SnO2/TiO2 composite system in relation to the bare SnO2. The present theoretical results may explain the growth of TiO2@SnO2 bimorph composite nanotape.
本研究关注TiO2/SnO2/TiO2和SnO2/TiO2/SnO2复合体系的结构和电子性质。采用了B3LYP水平的密度泛函理论的周期性量子力学方法。研究了TiO2/SnO2/TiO2和SnO2/TiO2/SnO2模型的(110)、(010)、(101)和(00)低指数金红石表面的弛豫表面能、结构特征和电子性质。为作比较，还对裸露的金红石TiO2和SnO2结构进行了分析，并与先前的理论和实验数据进行了比较。金红石TiO2和SnO2表面的计算表面能遵循(110) < (010) < (101) < (001)的顺序，对于SnO2/TiO2/SnO2和TiO2/SnO2/TiO2复合体系，能量分别按(010) < (101) < (110) < (001)和(010)近似=(110) < (101) < (001)的顺序增加。SnO2/TiO2/SnO2的表面能值比单个的SnO2和TiO2金属氧化物大，而TiO2/SnO2/TiO2体系的表面能值与TiO2处于同一量级且低于SnO2。对TiO2/SnO2/TiO2和SnO2/TiO2/SnO2体系的电子结构分析表明，所有研究表面价带上部的主要特征分别由外层主导，即分别由TiO2和SnO2主导，导带下部的拓扑结构类似于核心层。SnO2/TiO2/SnO2复合体系的(110)和(010)表面相对于其核心TiO2，价带顶和导带底都有能量稳定化，而对于TiO2/SnO2/TiO2复合体系的相同表面相对于裸露的SnO2则发现相反的趋势。目前的理论结果可能解释了TiO2@SnO2双晶复合纳米带的生长。
