Insulator-to-Metal Transition of Cr2O3 Thin Films via Isovalent Ru3+ Substitution
Insulator-to-Metal Transition of Cr2O3 Thin Films via Isovalent Ru3+ Substitution
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DOI：
10.1021/acs.chemmater.0c01497
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发表时间：
2020-05
影响因子：
8.6
通讯作者：
K. Fujiwara;M. Kitamura;D. Shiga;Y. Niwa;K. Horiba;T. Nojima;H. Ohta;H. Kumigashira;A. Tsukazaki
中科院分区：
文献类型：
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作者：
K. Fujiwara;M. Kitamura;D. Shiga;Y. Niwa;K. Horiba;T. Nojima;H. Ohta;H. Kumigashira;A. Tsukazaki
在过渡金属氧化物中，晶体结构和金属离子的广泛组合为调整其电子性质提供了肥沃的土壤。使用薄膜生长技术在人工异质结构中创建了与界面相关的额外自由度。然而，在刚玉类型和结晶学相关的三元化合物中，适用于晶格匹配电极层的氧化物的稀缺性经常阻碍这些异质结构的电学表征。在这里，我们报道了一种新型刚玉类氧化物薄膜的合成，这种薄膜具有金属导电性。用脉冲激光沉积的方法将Ru掺杂到反铁磁性绝缘体Cr2O3中，制备了块状未知的(Cr1-xRux)2O3薄膜。结构、电学和磁学表征表明，当Ru含量x大于约0.40时，反铁磁性绝缘体成为顺磁性金属，同时保留了主体刚玉结构。光谱分析表明，在费米能级上形成了Ru-4d衍生带，并且存在Ru3+，这是Ru在氧化物中很少观察到的价态。Ru~(3+)反常态的稳定归因于Cr2O_3骨架中的电荷中性约束以及动力学驱动的真空沉积过程。
In transition-metal oxides, the vast combinations of crystal structures and metal ions provide a fertile ground for tailoring their electronic properties. Using a thin-film growth technique creates an additional interface-related degree of freedom in the artificial heterostructures. However, in corundum-type and crystallographically related ternary compounds, the scarcity of oxides applicable to a lattice-matched electrode layer often impedes the electrical characterization of these heterostructures. Here, we report the synthesis of a thin film of a new corundum-type oxide that exhibits metallic conduction. By substituting Ru into the antiferromagnetic insulator Cr2O3 via pulsed laser deposition, we fabricated thin films of (Cr1–xRux)2O3 not known in bulk. The structural, electrical, and magnetic characterizations showed that the antiferromagnetic insulator became a paramagnetic metal at Ru contents x greater than approximately 0.40 while preserving the host corundum structure. Spectroscopic analyses revealed the formation of Ru 4d-derived bands at the Fermi level and the presence of Ru3+, which is a valence state of Ru rarely observed in oxides. The stabilization of the unusual Ru3+ state is attributed to the charge neutrality constraint in the robust Cr2O3-based framework as well as the kinetics-driven vacuum deposition process.