铁电SBN薄膜电光系数的测量及其在波导中的应用

利用溶胶-凝胶法在MgO(001)衬底上获得C轴择优取向的铁电铌酸锶钡(SBN)薄膜,主要介绍MgO(001)衬底上SBN60薄膜及掺入的K离子与Nb离子摩尔比例为1：3的SBN60薄膜横向电光系数r51的测量,实验测得不掺K的SBN60薄膜r51值为37．6pm／V,掺K的r51值为58．5pm／V。并由此设计一种基于MgO(001)衬底上的马赫一曾德尔型SBN60薄膜波导调制器,计算出在633nm时,掺K比例为1：3的此种波导调制器半波调制电压值为10V,不掺K的半波电压值为16V,结果说明掺入K离子能增加薄膜的横向电光系数并有效的减少波导的半波调制电压。     

Improvement of dielectric tunability and loss tangent of (Ba,Sr)TiO3 thin films with K doping

Ba_0.6Sr_0.4TiO₃ thin films doped with K were deposited on Pt/Ti/SiO₂/Si substrates by chemical solution deposition method. The structure, surface morphology, and dielectric and tunable properties of Ba_0.6Sr_0.4TiO₃ thin films have been studied in detail. The K content in Ba_0.6Sr_0.4TiO₃ thin films has a strong influence on the material's properties including surface morphology, dielectric and tunable properties. It is found that the Curie temperature of K-doped Ba_0.6Sr_0.4TiO₃ films shifts to higher values compared with that of undoped Ba_0.6Sr_0.4TiO₃ thin films, which leads to a dielectric enhancement of K-doped Ba_0.6Sr_0.4TiO₃ films at room temperature. At the optimized content of 0.02 mol, the dielectric loss tangent is reduced significantly from 0.057 to 0.020. Meanwhile, the tunability is enhanced obviously from 26% to 48% at the measured frequency of 1 MHz and the maximum value of the figure of merit is 23.8. This suggests that such films have potential applications for tunable devices.     

Investigations on the thermo-chemical stability and electrical conductivity of K-doped Ba3 − xKxCaNb2O9 − δ (x = 0.5, 0.75, 1, 1.25)

In this paper, we report the synthesis, crystal structure and electrical transport properties of new K-doped Ba₃CaNb₂O₉ (BCN) and investigate their chemical stability in H₂O and pure CO₂ at elevated temperature. The powder X-ray diffraction (PXRD) of Ba_2.5K_0.5CaNb₂O_9 − δ, Ba_2.25K_0.75CaNb₂O_9 − δ, Ba₂KCaNb₂O_9 − δ, and Ba_1.75K_1.25CaNb₂O_9 − δ showed the formation of a single-phase double perovskite (A₃BB^/₂O₉)-like cell with a lattice constant of a ∼ 2a_p (where a_p is a simple perovskite cell of ∼ 4 Å). Perovskite-like structure was found to be retained after treating with CO₂ at 700 °C and also after boiling H₂O for 120 h. The lattice constant of CO₂ and H₂O treated samples was found to be comparable to that of the corresponding as-prepared compound. The total electrical conductivity of all the investigated K-doped BCN increases with increasing K content in BCN in various atmospheres, including air, dry H₂, wet N₂ and wet H₂. The electrical conductivity in dry and wet H₂ atmospheres was found to be higher than that of air in the temperature range of 300-700 °C, while in wet N₂ a slightly lower value was observed. Among the compounds investigated in the present study Ba_1.75K_1.25CaNb₂O_9 − δ showed the highest total electrical conductivity of 1 × 10^− 3 S/cm in dry H₂ at 700 °C with an activation energy of 1.28 eV in the temperature range of 300-700 °C.     

Improvement of dielectric （Ba,Sr）TiO3 thin tunability and loss tangent of films with K doping

Ba0.6Sr0.4 TiO3 thin films doped with K were deposited on Pt/Ti/SiO2 /Si substrates by the chemical solution deposition method. The structure, surface morphology and the dielectric and tunable properties of Ba0.6Sr0.4 TiO 3 thin films have been studied in detail. The K content in Ba0.6Sr0.4TiO3 thin films has a strong influence on the material’s properties including surface morphology and the dielectric and tunable properties. It was found that the Curie temperature of K-doped Ba0.6Sr0.4 TiO3 films shifts to a higher value compared with that of undoped Ba0.6Sr0.4TiO3 thin films, which leads to a dielectric enhancement of K-doped Ba0.6Sr0.4 TiO3 films at room temperature. At the optimized content of 0.02 mol, the dielectric loss tangent is reduced significantly from 0.057 to 0.020. Meanwhile, the tunability is enhanced obviously from 26% to 48% at the measured frequency of 1 MHz and the maximum value of the figure of merit is 23.8. This suggests that such films have potential applications for tunable devices.     

Effect of sintering on the ionic conductivity of garnet-related structure Li5La3Nb2O12 and In- and K-doped Li5La3Nb2O12

Garnet-structure related metal oxides with the nominal chemical composition of Li₅La₃Nb₂O₁₂, In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ and K-substituted Li_5.5La_2.75K_0.25Nb₂O₁₂ were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li₅La₃Nb₂O₁₂. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In³⁺(r_CN6: 0.79 Å) for smaller Nb⁵⁺ (r_CN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K⁺ for La³⁺ and In³⁺ for Nb⁵⁺ in Li₅La₃Nb₂O₁₂ exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25-300 °C. Among the compounds investigated, the In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ exhibits the highest bulk lithium ion conductivity of 1.8×10⁻⁴ S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10⁻¹⁰-10⁻⁷ cm²/s over the temperature regime 50-200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li₅La₃Nb₂O₁₂ was found to be unsuccessful under the investigated conditions.