The conducting oxide (Ba,Sr)RuO3 (BSR), which offers an appropriate match in structure with (Ba,Sr)TiO3 (BST), was investigated as an interfacial layer to obtain a high tunability and high dielectric constant in BST films. The (100)-textured BST films deposited onto BSR interfacial layers showed smoother smaller grain size than those without BSR layers. The tunability and dielectric constant of the BST films increased with increasing BSR seed layer thickness and showed ∼70% tunability and a dielectric constant of 1300 at interfacial layer of 150 Å. The tunability and dielectric constant of BST films increased nearly two times and two and a half times, respectively, as much as that of BST films without BSR interfacial layers. The higher tunability and dielectric constant have been attributed to the suppression of low-dielectric layer formation and the reduced thermal stress by lattice mismatch.
The structural, microstructural, and surface morphological properties of Ba 0.5 Sr 0.5 TiO 3 thin films were investigated as a function of Ni dopant concentration. The Ni-dopant concentration in BST films has a strong influence on the material properties including dielectric and tunable properties as well as film growth rate. Ni doped (≤3 mol%) BST films showed denser, smoother, and smaller grain sizes than those with 6 and 12 mol% Ni. Dielectric constant and loss of 3 mol% Ni-doped BST films were about 980 and 0.3%, respectively. In addition, tunability and figure of merit of 3 mol% doped BST films showed maximum values of approximately 39% and 108, respectively. Correlation of the material properties with dielectric and tunable properties suggests the the 3 mol% Ni-doped BST films are the optimal choice for tunable device applications.
First principles calculations on the crystal and electronic structure of a layered Li(Ni 1/3 Mn 1/3 M 1/3 )O 2 (M = Al, Ti, Cr, Fe and Mo) were undertaken as part of a search for new positive electrode materials for advanced lithium ion batteries. The formal charge of Ni, Mn and M (Ti and Mo) were estimated to be +2, +3 and +4, respectively, from electronic structures and interatomic distances. In the cases of the Al, Cr and Fe substitution, the compounds had trivalent M and tetravalent Mn ions. The solid-state redox reactions of Li(Ni 1/3 Mn 1/3 M 1/3 )O 2 were calculated assuming a Li deinsertion scheme, and the reactions were shown to be Ni 2+ /Ni 3+ /Ni 4+ and M 3+ /M 4+ for the Cr and Fe substitution. Al substitution will lead to higher voltages, as fixed 3+ valence of Al forces more electron exchange with oxygen. The cases of Ti and Mo substitution, Ti and Ni ions do not participate in the redox reactions over the entire range, respectively. The substitutive cation-oxygen bonding has a more covalent character, when the redox energy of Ni is lowered, resulting in an increase in potential. As described above, the voltage profiles are very different because the types of metals are different and participate in electrochemical reactions according to the substituted.
The absence of a low dielectric constant layer at the barium strontium titanate (BST)/Pt interface and a decreased roughness are critical issues in the production of (Ba0.5Sr0.5)TiO3 thin films with high tunabilities and low losses. An improvement in dielectric properties was achieved by the insertion of seed layers at the BST/Pt interface by pulsed laser deposition. The higher tunability can be attributed to (100) texturing of the BST films, which is independent of grain size and grain morphologies, thus leading to a variation in seed layer thicknesses. The tunability and dielectric constant of 1600-Å-thick BST films showed a maximum of 53% and 720, respectively, at a seed layer thickness of 100 Å. Dielectric loss is dependent on the roughness of BST films and reached a minimum of 0.8% at a root mean square roughness of 28 Å. The maximum figures of merit, defined as the ratio of tunability to dielectric loss, of approximately 58 at 100 kHz and 198 kV/cm were obtained at a seed layer thickness of 70 Å. The optimized seed layer thickness for BST deposition onto Pt/Ti/SiO2/Si substrates plays an important role in maintaining the high tunabilities and low loss, which are suitable for microwave device applications.
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