用Ba(OH)2·8H2O和Sr(OH)2·8H2O配制电解液,工艺参数分别设置为电流密度20 A/dm2、电流频率100Hz、反应时间20 min及占空比85%,采用微弧氧化法在工业纯Ti板(99.5%)表面原位生长Ba x Sr(1-x)TiO3薄膜。分析了相同Ba2+/Sr2+比条...用Ba(OH)2·8H2O和Sr(OH)2·8H2O配制电解液,工艺参数分别设置为电流密度20 A/dm2、电流频率100Hz、反应时间20 min及占空比85%,采用微弧氧化法在工业纯Ti板(99.5%)表面原位生长Ba x Sr(1-x)TiO3薄膜。分析了相同Ba2+/Sr2+比条件下,电解液浓度对薄膜物相、表面形貌及薄膜厚度的影响。结果表明:所得薄膜均主要由四方相Ba0.5Sr0.5TiO3构成;Ba2+和Sr2+各为0.2 mol/L时所得薄膜的表面平整度及致密性最好,表面粗糙度值最小,并检测了该薄膜在不同频率下的介电常数和介电损耗,发现两者均随频率的增加而减小;薄膜厚度随电解液浓度的增加而增加。展开更多
Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators（FBARs） based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3（BST） fi...Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators（FBARs） based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3（BST） films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias（ 45 V） while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum（Mo） as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.展开更多
Ho^（3＋） doped La_（2（1-x））Yb_（2x）TiO_5 samples were prepared by sol-gel method. Pyrochlore structured powders were obtained under the annealing of the as-prepared samples at 1100 °C for 3 h in the air. Al...Ho^（3＋） doped La_（2（1-x））Yb_（2x）TiO_5 samples were prepared by sol-gel method. Pyrochlore structured powders were obtained under the annealing of the as-prepared samples at 1100 °C for 3 h in the air. All the samples were characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM） and photoluminescent spectroscopy. When x=0, we obtained La_2TiO_5 phosphors. Monitored at 546 nm, the excitation spectrum of Ho^（3＋） activated La_2TiO_5 phosphors consisted of a broad band originating from the charge-transfer band（CTB） between Ho^（3＋） ions and the nearest neighboring O^（2-） ions at 250-280 nm and four sharp bands associated to f-f transitions of Ho^（3＋） ions at 350-500 nm. Under the blue light excitation at 461 nm, Ho^（3＋） ion in La_2TiO_5 emitted an intense green emission band at 546 nm due to the transition of ~5S_2, ~5F_4→~5I_8. Two intense bands were observed at 490 nm（blue, ~5F_3→I_8） and 663 nm（red, ~5F_5→~5I_8） in the up-conversion（UC） spectrum under 980 nm NIR laser excitation in La_2TiO_5 phosphors activated with Ho^（3＋） alone, whereas they were much different from the down-conversion（DC） luminescent samples. When x=7.5 mol.%-17.5 mol.%, the UC emission spectra of them dominated at 546 nm（green, ~5S_2, ~5F_4→~5I_8） and enhanced significantly with the dose of Yb^（3＋） ion. The decay curve also confirmed that the transitions of ~5F_4→~5I_8 and ~5S_2→~5I_8 were merged into one emission band at 546 nm.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60871049 and 50972024)
文摘Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators（FBARs） based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3（BST） films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias（ 45 V） while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum（Mo） as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.
基金supported by the National Natural Science Foundation of China(51401130)the Natural Science Foundation of Liaoning Province(2014028015)Fundamental Research Foundation of Central Universities(N142304007)
文摘Ho^（3＋） doped La_（2（1-x））Yb_（2x）TiO_5 samples were prepared by sol-gel method. Pyrochlore structured powders were obtained under the annealing of the as-prepared samples at 1100 °C for 3 h in the air. All the samples were characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM） and photoluminescent spectroscopy. When x=0, we obtained La_2TiO_5 phosphors. Monitored at 546 nm, the excitation spectrum of Ho^（3＋） activated La_2TiO_5 phosphors consisted of a broad band originating from the charge-transfer band（CTB） between Ho^（3＋） ions and the nearest neighboring O^（2-） ions at 250-280 nm and four sharp bands associated to f-f transitions of Ho^（3＋） ions at 350-500 nm. Under the blue light excitation at 461 nm, Ho^（3＋） ion in La_2TiO_5 emitted an intense green emission band at 546 nm due to the transition of ~5S_2, ~5F_4→~5I_8. Two intense bands were observed at 490 nm（blue, ~5F_3→I_8） and 663 nm（red, ~5F_5→~5I_8） in the up-conversion（UC） spectrum under 980 nm NIR laser excitation in La_2TiO_5 phosphors activated with Ho^（3＋） alone, whereas they were much different from the down-conversion（DC） luminescent samples. When x=7.5 mol.%-17.5 mol.%, the UC emission spectra of them dominated at 546 nm（green, ~5S_2, ~5F_4→~5I_8） and enhanced significantly with the dose of Yb^（3＋） ion. The decay curve also confirmed that the transitions of ~5F_4→~5I_8 and ~5S_2→~5I_8 were merged into one emission band at 546 nm.
