利用微弧氧化法制备四方相BaTiO3薄膜的结构特征及铁电性能

利用微弧氧化技术在钛衬底上直接制备了四方相钛酸钡铁电薄膜.利用X射线(XRD)、HP4192A阻抗分析仪和铁电测试系统(FTS)等手段对薄膜样品的相结构、介电和铁电性能进行了研究.结果表明,工艺参数为Ba(OH)2浓度为0.5mol/L,电流密度为150mA/cm2,温度为57℃,反应时间5～20min的薄膜主要要由四方相BaTiO3构成.在微弧氧化过程中,弧点的连续移动是形成四方相BaTiO3的主要原因.此工艺参数下薄膜的剩余极化值为0.271和-4.62μC/cm2(Pr),与其对应的矫顽场强度分别为20和-2.8kV/cm(Ec).该薄膜具有良好的铁电性能.     

微弧氧化法制备BaTiO3薄膜的结构特性

利用微弧氧化技术在钛衬底上制备了钛酸钡铁电薄膜.利用x射线(XRD)、扫描电镜(SEM)和能谱仪(EDS)等手段研究了电流密度和电解液浓度对微弧氧化薄膜的化学成分、相组成、结构和表面形貌的影响.结果表明,随着电流密度和电解液浓度的增加,BaTiO3的形成能力增强,薄膜的致密度下降,表面粗糙度增加;当Ba(OH)2浓度为0.2 mol/l,电流密度为5 A/cm2,微弧氧化反应18 min后,可获得具有较高简单四方结构和底心正交结构BaTiO3含量的薄膜,且薄膜与衬底具有良好的结合性能.     

甘油含量对BaTiO3微弧氧化膜物相、组成及介电性能的影响

为进一步改进以Ba（OH）2为电解液的微弧氧化薄膜的性能,在Ba（OH）2溶液中加入不同含量的甘油,在工业纯钛板材（99．5％）表面微弧氧化生成了BaTiO2陶瓷膜。利用X射线衍射、扫描电镜、能谱和电容探测研究了甘油含量对陶瓷膜的物相、元素组成、表面形貌、薄膜厚度以及介电性能的影响。结果表明：不同甘油含量下制备的薄膜主要由四方相BaTi03构成;甘油的加入降低了薄膜的生长速率,改善了BaTiO2薄膜的表面形貌,提高了薄膜的介电性能;甘油添加量为2g／L时,薄膜具有较好的表面形貌和较高的介电常数。     

交/直流电源模式下BaTiO_3薄膜生长方式及微观结构研究

Ba(OH)2电解液中,分别采用交/直流源微弧氧化法在Ti基体表面制备了钛酸钡薄膜,并分别研究了两种薄膜的生长方式及微观结构。结果表明:交、直流源模式下所得Ba Ti O3薄膜的晶体结构分别主要由六方相、四方相构成;交流模式下薄膜从试样边角向中心呈层片状生长,直流模式下薄膜生长则主要依靠缓慢移动的连续电弧在膜层较薄弱区域发生的放电击穿;交流源模式下所得薄膜表面较平整、致密性较好;两种电流源模式下所得膜层均分布着大小不一的微弧氧化孔洞,但直流源模式下所得薄膜中孔洞分布较少。     

微弧氧化法生成四方相BaTiO3薄膜工艺研究

针对微弧氧化法生成四方相BaTiO3薄膜的工艺参数影响规律进行研究.将Ti板置于含Ba2+的电解液中在0.15～0.55mol/L和1.0～5.5A的浓度、电流区域内进行微弧氧化.实验发现微弧只在一定的浓度-电流区域中发生,可用平面图直观表示;在不同的浓度-电流区域内,薄膜具有不同的形貌,据此将浓度-电流区域图进一步划...     

SiO_2表面包覆改性钛酸钡/聚酰亚胺复合薄膜的制备与性能

以聚酰亚胺(PI)为基体,将聚酰亚胺与钛酸钡(BaTiO3)纳米粒子进行复合,采用原位聚合法制备BaTiO3/PI复合薄膜。为提高BaTiO3纳米粒子的分散性和表面性能,采用SiO2对BaTiO3纳米粒子进行表面包覆改性,并制备改性BaTiO3/PI复合薄膜。采用红外光谱、X射线衍射、扫描电镜等对制备得到的改性BaTiO3进行了表征,测试了复合薄膜的介电性能。结果发现,SiO2与BaTiO3粒子间仅是物理包覆,没有新物质形成。测试频率为103 Hz时,质量分数为5%的SiO2包覆改性使复合薄膜的介电常数增大到21.8,介电损耗为0.00521,击穿强度为76 MV/m,储能密度为0.56J/cm3。研究表明,采用SiO2对BaTiO3改性使得复合薄膜的介电性能有所提高。     

激光分子束外延BaTiO3/SrTiO3超晶格的晶格应变研究

采用脉冲激光分子束外延(PLMBE)方法,通过优化的工艺参数,在SrTiO3(100)单晶基片上外延结构为(8/8)的BaTiO3/SrTiO3超晶格薄膜.综合利用反射式高能电子衍射系统(RHEED)、高分辨率X射线衍射(HRXRD)以及高分辨率透射电镜选区电子衍射(SAED)技术,研究超晶格薄膜的晶格应变现象和规律.研究结果表明,在制备的BaTiO3/SrTiO3超晶格薄膜中,BaTiO3晶胞面外晶格增大,面内晶格减小;而SrTiO3晶胞面内及面外方向晶格都被拉伸,但面外晶格拉伸程度较大,SrTiO3晶胞产生了与BaTiO3晶胞方向一致的四方相转变.     

微弧氧化生成钛酸盐系铁电薄膜研究

为开发新的铁电薄膜制备工艺,需将Ti板微弧氧化.采用Ba(OH)2、Ba(CH3COO)2、BaCl2、Ba(OH)2+Ba(NO3)2及Pb(CH3COO)2对Ti板进行微弧氧化试验,并对生成的薄膜进行物相组成和显微形貌的分析.结果表明:Ti板在BaCl2、Pb(CH3COO)2及Ba(OH)2+Ba(NO3)2中不...     

硫酸铜浓度对镁合金微弧氧化膜层热控性能的影响

为了提高镁合金的热防护性能,在硅酸盐、磷酸盐、铝酸盐等电解液体系中引入硫酸铜,采用微弧氧化技术在MB15镁合金表面制备微弧氧化膜层。通过扫描电镜(SEM)、X射线衍射仪(XRD)、能谱仪(EDS)和CIE颜色系统研究了电解液中硫酸铜浓度对涂层的色度、厚度、粗糙度和热控性能的影响。结果表明:微弧氧化膜层微观上具备典型的多孔结构,铝酸盐涂层主要由MgAl_2O_4晶相组成,硅酸盐涂层主要由MgO晶相和Mg_2SiO_4晶相组成,磷酸盐涂层主要由MgO晶相组成,而各膜层中的Cu元素均以非晶相形式存在;随着硫酸铜浓度增加,3种体系制备的膜层表面颜色均向黑色过渡,微孔数量增多;硅酸盐体系和磷酸盐体系中制备的微弧氧化膜层具有高吸收率和高发射率等特点,而铝酸盐体系中制备的微弧氧化膜层具有高吸收率和低发射率的特点。     

BaTiO3铁电薄膜的光致发光研究

以分析纯的乙酸钡和钛酸正四丁酯为前躯体溶液,冰乙酸为溶剂,乙酰丙酮为稳定剂,采用溶胶-凝胶法在硅基上制备了钛酸钡(BaTiO3)铁电薄膜.研究了BaTiO3铁电薄膜的光致发光性能.结果表明,室温下非晶态的BaTiO3铁电薄膜在蓝光激发下具有很强的光致发光现象.其中,经8h 673K退火处理的非晶BaTiO3铁电薄膜的光致发光性能最佳,当455nm光激发时,非晶薄膜在540～660nm内发出强烈的黄光,峰值波长为580～610nm,峰宽约30nm,发光强度随薄膜的厚度增加而增强.晶态BaTiO3铁电薄膜无任何发光现象.     

四方相BaTiO3薄膜的自组装制备与表征

以(NH₄)₂TiF₆、 Ba(NO₃)₂ 和H₃BO₃为主要原料, 采用自组装单层膜(SAMs)技术, 以三氯十八烷基硅烷(octadecyl-trichloro-silane, OTS)为模版, 在玻璃基片上制备了四方相钛酸钡晶态薄膜. 改性基板的亲水性测定与原子力显微镜（AFM）测试表明, 紫外光照射使基板由疏水转变为亲水, 能够对OTS-SAM起到修饰作用. 金相显微镜观察结果显示,OTS单分子膜指导沉积的薄膜样品表面均匀, 表明OTS SAM对钛酸钡薄膜的沉积具有诱导作用; X射线衍射（XRD）与扫描电镜（SEM）表征显示, 空气中600℃下保温2h实现了薄膜由非晶态向四方相BaTiO₃晶态薄膜的转化过程, 制备的钛酸钡薄膜在基板表面呈纳米线状生长, 线长约在500～1000nm之间, 相互连接的晶粒大小约为100nm. 文章同时对自组装单层膜和钛酸钡薄膜的形成机理进行了探讨.     

Barium titanate thin films deposited by electrophoresis on p-Doped Si (001) substrates

Barium titanate (BaTiO3) thin films have been prepared by electrophoretic deposition on p-doped and platinum covered silicon (Si) substrates. Their structure, nanostructure and dielectric properties were characterized. The as-deposited films were polycrystalline and composed by barium titanate nanograins with an average grain size approximately 9 nm. Annealing at high temperatures promoted grain growth, so that the samples annealed at 600 degrees C presented average grain sizes approximately 24 nm. From Raman spectroscopy measurements it was found that the tetragonal (ferroelectric) BaTiO3 phase was stabilized on the films. Also, at higher annealing temperatures, cation disorder was reduced on the films. From measurements of the temperature dependence of the dielectric permittivity the corresponding paraelectric-ferroelectric phase transition was determined. The observed transition temperature (approximately 100 degrees C) was found to be below the BaTiO3 bulk or thick film values, due to the small nanosized grains composing the films.     

Microwave assisted semi-solvothermal synthesis of nanocrystalline barium titanate

In an endeavor to synthesize tetragonal nanocrystallites of BaTiO3 at much reduced reaction time, we explored the possibility of performing microwave assisted semi-solvothermal reaction by using Ba(OH)2 . 8H2O and amorphous titanium hydrous gel as precursors and 1,4-butanediol and water as solvent. Typically, such a microwave assisted reaction was accomplished within 2 hrs at 220 degrees C as against 12 hrs required in conventional approach. The crystallized BaTiO3 powders (microwave assisted as well as conventionally processed for reference) were characterized by X-ray diffraction, thermal analysis, infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. We have detected metastable cubic phase by XRD while locally symmetric tetragonal phase by Raman spectroscopy in case of conventional semi-solvothermal processing. On the contrary, we could detect co-existence of tetragonal and cubic phases by XRD and only tetragonal phase by Raman spectroscopy in case of microwave assisted semi-solvothermal processing. The TEM analysis indicates typical particle size distribution in the range of approximately 20 to 80 nm for conventionally processed powder while that in the range of approximately 20 to 50 nm for microwave processed powder. HRTEM images evince the distortion from an ideal cubic structure in case of microwave processed powder which can be correlated with anisotropic lattice contraction during the microwave induced heating. AFM analysis exhibited relatively less aggregation of nanoparticles for microwave assisted process.     

Microstructure evolution during annealing of an amorphous TiAl sheet

An amorphous, 150 μm thick freestanding sheet of a TiAl-based alloy was produced by physical vapor deposition (PVD). The following phase transformations were observed after different stages of crystallization of the amorphous sheet and analyzed using differential thermal analysis, X-ray diffraction, and transmission electron microscopy: amorphous→body centered cubic (β)→hexagonal close-packed ()?→tetragonal (γ)+ordered ₂. The β phase was formed as near-spherical particles that were evenly distributed in the amorphous phase and the size of these particles was approximately 90 nm. Formation of the phase by decomposition of β and the remaining amorphous phases led to a very fine feathery-like microstructure arranged in colonies of approximately 100 nm in size. Interface boundaries between the phase particles were poorly defined. The transformation of the metastable phase into a mixture of the γ and ₂ phases led to formation of an equiaxed γ-grain structure with the grain size of approximately 150 nm.     

The effects of substrates on the thin-film structures of BaTiO3

Barium titanate (BaTiO₃) thin films prepared on magnesia, silicon and strontium titanate substrates by r.f. sputtering has been investigated. As a function of substrate and annealing temperatures, the crystal structure and shape were examined by X-ray diffraction and scanning electron microscopy. Thin films were grown on both MgO and silicon substrates; they were amorphous when deposited on MgO if the substrate temperature was less than 450 °C, while for those grown on silicon the temperature had to be less than 500 °C. Above these elevated temperatures, the films were crystalline, with cubic symmetry. After annealing the thin films on magnesia, the crystal structure changed from cubic to tetragonal phase above 1100 °C; thebe c-axis or annealing thus caused the grain growth of the BaTiO₃. The thin films on SrTiO₃ were found toc-axis oriented tetragonal films for a substrate temperature above 500 °C.     

富氮MeNx(Me=Ti,Zr,Hf)薄膜的结构与红外光学性能

用射频反应磁控溅射方法制备了MeNx(Me=Ti、Zr、Hf)薄膜,研究了在富N2条件下不同的N2/Ar流量比对薄膜结构和光学性能的影响.掠角X射线衍射的分析结果表明,所制得的富氮的TiNx薄膜主要由TiN所组成,而富氮的ZrNx、HfNx薄膜则具有非晶态的结构.用分光光度计和傅里叶红外仪对薄膜的光学透过率的测试表明,...     

Ferroelectric hollow particles obtained by solid-state reaction

Hollow particles of barium titanate were obtained by a two-step process combining colloidal chemistry and solid-state reaction. BaCO(3) crystals (size ≈1?μm) suspended in a peroxy-Ti(IV) aqueous solution were coated with an amorphous TiO(2) shell using a precipitation process. Calcination of the BaCO(3)@TiO(2) core-shell particles at 700?°C resulted in the formation of BaTiO(3) hollow particles (shell thickness of ≈70?nm) which retain the morphology of the BaCO(3) crystals. Formation of the cavity occurs because out-diffusion of the core phase is much faster than in-diffusion of the shell material. X-ray diffraction (XRD) and Raman spectroscopy indicate that the hollow particles possess a tetragonal ferroelectric structure with axial ratio c/a = 1.005. Piezoresponse force microscopy has shown strong piezoactivity and 180° ferroelectric domains. The process described provides a general route to fabricate hollow ferroelectric structures of several compounds.     

Crystallization of amorphous Te-20 at% Sn alloy

Amorphous Te-20 at% Sn alloy was obtained by rapid cooling from the liquid state. Phase transitions occurring during continuous heating of amorphous films were studied by differential thermal analysis, X-ray diffraction and transmission electron microscopy. It was found that the crystallization of the amorphous phase begins at 382 K and proceeds via nucleation and growth of metastable phases MS1 and MS2. The first of these phases was assigned the primitive cubic structure with lattice parameter a=3.2Å. The second phase, being a Te (Sn) solution, was assigned the hexagonal structure with lattice parameters a=4.45Å and c=5.85Å. During heating at 410 K the remaining amorphous phase decomposed into a mixture of Te crystals together with metastable phase MS3, which probably has the ZnS type structure with lattice parameter a=6.05Å. Within the temperature range 450 to 550 K the MS1 phase was transformed into SnTe, and the MS2 phase into Te. The metastable intermediate phase MS3 decomposed only near the solidus temperature, and the alloy attained its equilibrium structure.     

Crystalline carbon nitride films prepared by microwave plasma chemical vapour deposition

Crystalline carbon nitride films have been synthesized on Si (100) substrates by a microwave plasma chemical vapour deposition technique, using mixture of N₂, CH₄ and H₂ as precursor. Scanning electron microscopy shows that the films consisted of hexagonal bars, tetragonal bars, rhombohedral bars, in which the bigger bar is about 20 μm long and 6 μm wide. The X-ray photoelectron spectroscopy suggests that nitrogen and carbon in the films are bonded through hybridized sp² and sp³ configurations. The x-ray diffraction pattern indicates that the films are composed of α-, β-, pseudocubic and cubic C₃N₄ phase and an unidentified phase. Raman spectra also support the existence of α- and β-C₃N₄ phases. Vickers microhardness of about 41.9 GPa measured for the films.