Dielectric Characteristics of Ba0.65Sr0.35TiO3 Thin Films by Sol-Gel Method

Ferroelectric Ba0.65Sr0.35TiO3 (BST) thin films on the Pt/Ti/SiO2/Si substrate have been successfully prepared by sol-gel. Such films have approximately 300 nm thicknesses with a remnant polarization of about 2.95 C/cm2 and a coercive field of about 21.5 kV/cm. The investigations of X-ray diffraction and atomic force microscopy show that the BST films annealed at 650 ℃ exhibit a tetragonal structure and that the films dominantly consist of large column or grains of about 89 nm in diameter. The curves of the temperature dependence of dielectric coefficient in different frequencies display the curie transition at the temperature around 23 ℃. The dielectric loss tangent of BST thin films at 100 kHz is less than 0.04. As a result, the BST thin films are more applicable for fabrication of infrared detector compared with the BST thin films reported previously.     

Bi元素对钛酸锶钡薄膜结构与性能影响的研究

研究了微量元素铋对Sr0.5Ba0.5-xBixTiO3薄膜介电性能的影响.当X分别为0～0.030 mol时,相对介电常数εr、介质损耗tanδ逐渐降低,最大介电常数温度点Tm(居里温度点)逐渐移向低温;在所测试频率范围内,εr、tanδ均能表现出较好的频散特性;当铋掺量为0.015mol时,薄膜的Pr为0.22μC/cm2、Ps为0.32μC/cm2、Ec为60kV/cm.采用XRD、FTIR、TEM等测试方法分析了薄膜的结构特征.薄膜的矿物组成为四方钙钛矿结构,但[TiO6]八面体特征吸收峰(471.65cm-1)移向低波数,晶粒粒径减小.     

(Ba,Sr)TiO3 solid solutions sintered from sol-gel derived powders: An insight into the composition and temperature dependent dielectric behavior

Single-phase Ba_1-xSr_xTiO₃ (BST) perovskite ceramics with 0.3 ≤ x ≤ 0.4 were prepared from powders synthesized via sol-gel route. The compositions have the ferroelectric-paraelectric phase transition close to room temperature. At 20 ^°C the BST ceramics are ferroelectric for 0.3 ≤ x ≤ 0.35 and paraelectric for x = 0.375 and x = 0.40. The study follows the relation between the structural changes produced when increasing the Sr content and the dielectric properties at low intensity electric fields. It is found that the grain size and tetragonality decreases as the Sr content increases. Analyses of complex permittivity and impedance spectroscopy reveal the temperature and frequency dependencies of the dielectric properties. The phase transitions seem to be of first order for all compositions, with a thermal hysteresis that decreases with increasing the Sr content, fact attributed to the corresponding increase of the grain boundaries weight allowing a more efficient stress relaxation in the structure during the change of the symmetry from cubic to tetragonal. The diffusiveness degree during the phase transition is increasing with Sr content, suggesting some relaxor-type contribution attributed to smaller grain size. The ac conductivity follows the universal Jonscher law, with an ac component having the power parameter s independent of Sr content, and a dc component that it is thermally activated with an activation energy of about 0.7–0.77 eV attributed to oxygen vacancies acting as donor-like defects. The fit of impedance spectra at different temperatures and frequencies is obtained by using an equivalent circuit accounting the grains, grain boundaries, electrode interfaces and the local contributions produced by reorientation of defect dipoles or defect clusters. All the component circuits have significant variations around phase transitions. These are discussed in relation to structural changes occurring during transition and considering the changes in the distribution of various charges when polarization vanishes.     

Enhancement of relaxor properties by Nb doping in Ba0.8Sr0.12Ca0.08TiO3 lead-free ferroelectric ceramics

Niobium-doped barium strontium calcium titanate (BSCTN) ceramics were prepared using a conventional solid-state reaction method. The effects of Nb contents on crystal structure, microstructure, dielectric properties and ferroelectric relaxor behavior of the BSCTN ceramics were investigated. The BSCTN ceramics showed dense microstructures with uniform crystal grains with Nb doping. It was demonstrated that Nb⁵⁺ entered the B-site of the perovskite BSCTN ceramic and substituted for Ti⁴⁺, which caused the expansion and distortion of crystal lattice of the tetragonal BSCTN ceramic. Doping of Nb resulted in more diffused phase transition and lower Curie temperature of the BSCTN ceramics. The diffuseness degree indicator γ increased until the addition of Nb dopant exceeded 1.5 mol% where a maximum γ of 1.98 was achieved. Among the compositions assayed in this work, the BSCTN ceramics with Nb contents of approximately 1.0–1.5 mol% yielded promising relaxor properties that made them alternative sources for development of environmental friendly lead-free relaxor ferroelectric materials.     

Dielectric and energy storage properties of Mn-doped Ba0.3Sr0.475 La0.12Ce0.03TiO3 dielectric ceramics

Microstructure, temperature and frequency dependent dielectric and energy storage properties of Ba_0.3Sr_0.475La_0.12Ce_0.03Ti_1−xMn_xO₃(x = 0 − 0.005) have been investigated with X-ray diffractometer, and scanning electron microscope, broad band dielectric spectrometer and ferroelectric analyzer. The doping of Mn substantially decreased the dielectric loss, but made some of Ce³⁺ be oxidized to Ce⁴⁺ entering into B-site, which resulted in the formation secondary phases. For the Mn-doped composition, extremely low dielectric loss (10⁻⁵ order of magnitude at 10 kHz) could be obtained at room temperature. The relaxation mechanism at low temperature is of the dipole type for the undoped composition and that at high temperature (>500 K) is governed by the trap controlled ac conduction, respectively. The energy storage properties were improved by the doping with Mn due to the increase of insulation. Maximum energy density of 0.953 J/cm³ could be obtained for x = 0.003 composition with the BDS of 247 kV/cm and efficiency of 93%.     

铁电薄膜热释电非致冷红外传感器研究

阐述了铁电薄膜热释电非致冷红外传感器的工作原理,对铁电薄膜材料的要求及sol-gel铁电薄膜电性能。研究了BST铁电薄膜红外传感器的制备工艺与测试方法。研制出单元和8元、9元、10元线列铁电薄膜热释电非致冷红外传感器。     

Synthesis and diffused phase transition of Ba0.7Sr0.3TiO3 ceramics by a reaction-sintering process

Ba_0.7Sr_0.3TiO₃ (BST) ceramics prepared by a reaction-sintering process were investigated. BST ceramics could be obtained after 2–6 h sintering at 1330–1370 °C without any calcination involved. BST with density 5.68 g/cm³ (99.8% of the theoretic value) was obtained at 1350 °C for 6 h sintering. Grains of 2–15 μm were formed after 2–6 h sintering at 1330–1370 °C. A diffused ferroelectric–paraelectric transition was observed in pellets sintered at 1330 °C for 2 h and disappeared at a longer soak time or a higher sintering temperature.     

组分梯度（Ba,Sr）TiO3薄膜的制备工艺研究

采用改进的溶胶．凝胶（sol-gel）法在si衬底上制备了组分梯度Ba1-xSrxTiO3（x=0，0．1，0．2，0．3，0．4）（简称BST）薄膜。探讨了不同退火温度对组分梯度BST薄膜晶化的影响，应用X射线衍射（XRD）及原子力显微镜（AFM）分析了薄膜的微观结构。结果表明组分梯度薄膜的最佳制备工艺为600℃预烧5min，700℃退火1．5h，此时薄膜具有完整的钙钛矿相，薄膜表面平整、无裂纹、无孔洞。比较了单组分和组分梯度BST薄膜的微观结构。XRD测试结果显示，组分梯度BST薄膜的衍射峰峰位介于底层和硕层单组分BST薄膜之间，且衍射峰明显宽化；AFM测试结果表明，组分梯度BST薄膜的晶粒明显大于单组分BST薄膜，表面均方根粗糙度（RMS）也大于单组分BST薄膜，这可能是由于组分梯度薄膜较高的预烧温度促进晶粒生长造成的。     

Dielectric Characteristics of Ba_(0.65)Sr_(0.35)TiO_3 Thin Films by Sol-Gel Method

Ferroelectric Ba0.65Sr0.35TiO3(BST) thin films on the Pt/Ti/SiO2/Si substrate have been successfully prepared by sol-gel. Such films have approximately 300 nm thicknesses with a remnant polarization of about 2.95 μC/cm2 and a coercive field of about 21.5 kV/cm. The investigations of X-ray diffraction and atomic force microscopy show that the BST films annealed at 650 °C exhibit a tetragonal structure and that the films dominantly consist of large column or grains of about 89 nm in diameter. The curves of the temperature dependence of dielectric coefficient in different frequencies display the curie transition at the temperature around 23 °C. The dielectric loss tangent of BST thin films at 100 kHz is less than 0.04. As a result,the BST thin films are more applicable for fabrication of infrared detector compared with the BST thin films reported previously.     

LSMCD法制备梯度BST铁电薄膜的工艺研究

研究了利用液态源雾化化学沉积(LSMCD)法制备梯度钛酸锶钡(BST)薄膜的工艺。该方法既可以较精确的控制薄膜的化学计量比及掺杂浓度,又可采用控制超声雾化沉积的时间和次数来有效的控制膜厚及晶粒的大小。X-射线衍射(XRD)和扫描电镜(SEM)分析表明:沉积8次,采用常规退火方式,在Pt/Ti/SiO2/Si衬底上能成功制备出具有钙钛矿结构的、晶粒粒径约80 nm、厚约850 nm的梯度BST薄膜。该BST梯度薄膜在常温下介电常数达526,介电损耗约为0.06,矫顽场强约为100 kV/cm,剩余极化强度约为10μC/cm2,饱和极化强度约为20μC/cm2,在各个领域都具有广阔的应用前景。