Structural and ferroelectric properties of the caxis oriented SrBi2Ta2O9 thin films deposited by the radio frequency magnetron sputtering
Layered structure SrBi2Ta2O9 thin films were grown on Pt/Ti/Si/SiO2 substrates by laser ablation. The films were deposited at temperatures ranging from 500 to 750 °C and characterized for their phase formation, morphology, surface composition, and ferroelectric properties. Although crystalline phase formation was observed at temperatures as low as 500 °C, well defined saturated hysteresis loops were observed only in films deposited at temperatures of 700 °C or above. The transition in ferroelectric properties between 650 and 700 °C was associated with a change in orientation and grain size. The orientation of the films changed from highly c‐axis oriented at 650 °C to randomly polycrystalline at 700 °C, while the grain size of the films increased from an average value of 80 nm (at 650 °C) to 160 nm (at 700 °C). An understanding of process‐structure relationships is required in order to fabricate high quality films at lower temperatures.
A liquid source metal-organic chemical vapor deposition system was installed to deposit SrBi 2 Ta 2 O 9 (SBT) thin films on sapphire and Pt͞Ti͞SiO 2 ͞Si substrates. The process parameters such as deposition temperature and pressure, and ratio of Sr : Bi : Ta in the precursor solutions were optimized to achieve stoichiometric films with good reproducible ferroelectric properties. It was found that the nucleation of SBT started at a deposition temperature close to 500 ± C and grain growth dominated at 700 ± C and higher temperatures. With increasing deposition temperatures, the grain size of SBT thin films increased from 0.01 mm to 0.2 mm; however, the surface roughness and porosity of the films also increased. To fabricate specular SBT films, the films had to be deposited at lower temperature and annealed at higher temperature for grain growth. A two-step deposition process was developed which resulted in high quality films in terms of uniformity, surface morphology, and ferroelectric properties. The key to the success of this process was the homogeneous nucleation sites at lower deposition temperature during the first step and subsequent dense film growth at higher temperature. The two-step deposition process resulted in dense, homogeneous films with less surface roughness and improved ferroelectric properties. SBT thin films with a grain size of about 0.1 mm exhibited the following properties: thickness: 0.16-0.19 mm; 2P r : 7.8 -11.4 mC͞cm 2 at 5 V; E c : 50-65 kV͞cm; I leakage : 8.0 -9.5 3 10 29 A cm -2 at 150 kV͞cm; dielectric constant: 100 -200; and fatigue rate: 0.94-0.98 after 10 10 cycles at 5 V.
This study aimed at investigating the influence of microstructure on mechanical properties of Harmonic Structured (HS) pure-Ni compacts. The harmonic structure is a heterogeneous microstructure with a spatial distribution of fine grains (FG) and coarse grains (CG), that is, the CG areas ('Core') embedded in the matrix of three-dimensionally continuously connected network of FG areas ('Shell'). The HS pure-Ni samples were fabricated by powder metallurgy route consisting of mechanical milling (MM) of plasma rotated electrode processed pure-Ni powder and subsequent sintering by Spark Plasma Sintering. The plastic deformation at powder particle surface increases with increasing MM time. As a result, after sintering, shell fraction also increases in the HS pure-Ni samples. It was found that the fraction of a "shell" area is an important parameter controlling the balance of the mechanical properties of the HS pure-Ni compacts. The HS pure-Ni with a higher fraction of "shell" area demonstrated higher strength and approximately similar elongation as compared to the homo Ni samples and HS pure-Ni samples containing low shell fraction. Moreover, the effects of strain hardening rates and strain hardening exponents on deformation behaviour of HS pure-Ni samples were also discussed.
Quantum feedback control protocols can improve the operation of quantum devices. Here we examine the performance of a purification protocol when there are imperfections in the controls. The ideal feedback protocol produces an x-eigenstate from a mixed state in the minimum time, and is known as rapid state preparation. The imperfections we examine include time delays in the feedback loop, finite strength feedback, calibration errors and inefficient detection. We analyse these imperfections using the Wiseman-Milburn feedback master equation and related formalism. We find that the protocol is most sensitive to time delays in the feedback loop. For systems with slow dynamics, however, our analysis suggests that inefficient detection would be the bigger problem. We also show how system imperfections, such as dephasing and damping, can be included in a model via the feedback master equation.
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