Local structure of Ta-Re mixed oxide thin films studied by x-ray absorption spectroscopy

Mixed Ta-Re oxide thin films were synthesised for the first time by dc magnetron co-sputtering. Local environment around tantalum and rhenium atoms was studied by the Ta and Re L₃-edges x-ray absorption spectroscopy in pure Ta₂O₅ and mixed Ta-Re oxide thin films (Ta:Re= 50:50, 38:62, 20:80 as determined from the ratio of the Ta-to-Re absorption edges). It was found that rhenium atoms are four-fold coordinated by oxygen atoms with R(Re-O)=1.74±0.01 Å and the mean square relative displacement (MSRD) σ²=0.0012±0.0005 Å ². In pure Ta₂O₅ thin film, tantalum ions are coordinated by six oxygen atoms at R(Ta-O)=2.02±0.01 Å with the MSRD σ²0.010±0.0001 Ų. The addition of rhenium ions shortens the Ta-O distance by about 0.02-0.03 Å and makes the Ta-O distances distribution slightly broader with the MSRD σ ²≈0.013±0.001 Ų. The high frequency contribution in the Ta L₃-edge EXAFS signals, which is responsible in its Fourier transform for the peak beyond the first coordination shell, is due to the multiple-scattering effects within distorted [TaO₆] octahedron.