Abstract
Sm0.5Nd0.5NiO3 (SNNO) films with metal-insulator transition (MIT) at room-temperature (∼300 K) have been grown on NdGaO3 (001) substrates by pulsed laser deposition. By modifying the parameters of oxygen pressure, substrate temperature, and film thickness, the role of oxygen vacancies and strain relaxation on the MIT of SNNO films was systematically analyzed. The strain status of the films was carefully characterized by means of high resolution x-ray diffraction. The results revealed that for the fully strained films (≤20 nm) an increment of deposition oxygen pressure (and/or temperature) would decrease the content of oxygen vacancies and Ni2+ in the films, leading to a sharp MIT. In contrast, the strain relaxation occurs in the thicker films (>20 nm) despite an optimized oxygen pressure (temperature) was adapted for the deposition, which results in an inferior transport property and surface morphology. Specifically, a broadening MIT and a doublet TMI was observed in the partially strained films, where one TMI kept a stable value around 300 K in analogues to that of fully strained film, and another one increased with the increment of the film thickness, reaching a highest value of 330 K. This might be induced by the coexistence of a fully strained part and a strain-relaxed portion in the thicker films that observed on high resolution X-ray reciprocal space mappings.
Highlights
INTRODUCTIONIt has been shown that pulsed laser deposition (PLD) can be used to prepare NdNiO3 thin films under relatively mild conditions without the need for a postannealing under high oxygen pressure, owing to the production of Ni3+ ions in the plume during deposition.[11,12] This facilitates tuning a room temperature TMI in R1−xNdxNiO3 film (ion size of R is smaller than that of Nd) with moderate conditions, as showing in Y0.2Nd0.8NiO3 film of 50 nm thick grown on NdGaO3 (110) substrate, which exhibited a TMI at 302 K.13
The nickelates with the generic formula RNiO3 are of high interesting for devices applications such as modulated switches, sensors, and thermochromic coating, due to their sharp metal-insulator transition (MIT) versus temperature.[1,2] They crystallize in the orthorhombic perovskite structure and display MIT temperature of TMI = 130, 135, 200, 400, 450 and 560 K for R = Y, Pr, Nd, Sm, Eu, and Ga, respectively.[2]
SNNO films with MIT at room temperature are successfully prepared on NGO (001) substrates by pulsed laser deposition
Summary
It has been shown that pulsed laser deposition (PLD) can be used to prepare NdNiO3 thin films under relatively mild conditions without the need for a postannealing under high oxygen pressure, owing to the production of Ni3+ ions in the plume during deposition.[11,12] This facilitates tuning a room temperature TMI in R1−xNdxNiO3 film (ion size of R is smaller than that of Nd) with moderate conditions, as showing in Y0.2Nd0.8NiO3 film of 50 nm thick grown on NdGaO3 (110) substrate, which exhibited a TMI at 302 K.13. We report on fabrication of epitaxial Sm0.5Nd0.5NiO3 (SNNO) films on (001) NdGaO3 (NGO) substrates with TMI near room temperature by PLD. The growth conditions such as oxygen pressure, substrate temperature, and thickness were varied to investigate their influences on the MIT characteristics. These two steps enable us to analyze the role of oxygen vacancies and the strain relaxation on the MIT separately
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