Structural and ferroelectric properties of La modified Sr0.8Bi2.2Ta2O9 thin films

La modified SBT (Sr_0.8La_0.1Bi_2.1Ta₂O₉) thin films of different thickness were fabricated on Pt/Ti/SiO₂/Si substrates by the metalorganic decomposition technique. All the films were annealed layer-by-layer at 800 °C using a rapid thermal annealing furnace. X-ray diffraction analysis indicated that the relative intensity of the (2 0 0) diffraction peak [I(2 0 0)/I(1 1 5)] increased with the increase of the film thickness. Eventually, an a-axis preferentially oriented SLBT film was obtained. These results are discussed with respect to the anisotropy of the grain growth. The a-axis preferentially oriented SLBT film, whose relative intensity of the (2 0 0) peak [I(2 0 0)/I(1 1 5)] was 1.05, had a remanent polarization (2P_r) value of 21 μC/cm² and a coercive field (2E_c) value of 70 kV/cm under the electric field of 200 kV/cm.     

Dielectric properties of (Ba,Ca)(Zr,Ti)O3/CaRuO3 heterostructure thin films prepared by pulsed laser deposition

(Ba_0.90Ca_0.10)(Zr_0.25Ti_0.75)O₃ (BCZT) thin films were grown on Pt/Ti/SiO₂/Si substrates without and with a CaRuO₃ (CRO) buffer layer using pulsed laser deposition (PLD). The structure and surface morphology of the films have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). At room temperature and 1 MHz, the dependence of dielectric constant and tunability of the films with electric field were investigated; the dielectric constant and tunability are 725 and 47.0%, 877 and 50.4%, respectively, for the BCZT film on Pt/Ti/SiO₂/Si substrates without and with the CRO buffer layer at 400 kV/cm. The tunability of the BCZT/CRO heterostructure thin films on Pt/Ti/SiO₂/Si substrates was higher than that of the BCZT thin films on Pt/Ti/SiO₂/Si substrates. The high constant likely results from the oxide electrode (CRO).     

The synthesis of lead-free ferroelectric Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3 thin films by sol-gel method

(1 − x)Bi_0.5Na_0.5TiO₃-xBi_0.5K_0.5TiO₃ [BNT-BKT-100x] thin films have been successfully deposited on Pt/Ti/SiO₂/Si substrates by a sol-gel process together with rapid thermal annealing. A morphotropic phase boundary (MPB) between Bi_0.5Na_0.5TiO₃ and Bi_0.5K_0.5TiO₃ was determined around x ∼ 0.15. Near the MPB, the film exhibits the largest grain size, the highest ε value (360) and the largest P_r value (13.8 μC/cm²). The BNT-BKT thin film system is expected to be a new and promising candidate for lead-free piezoelectric applications.     

Pulsed laser deposition optical waveguiding Bi3TiNbO9 thin films on fused silica

The layered-perovskite ferroelectric Bi₃TiNbO₉ (BTN) optical waveguiding thin films have been prepared on fused silica substrates by pulsed laser deposition (PLD). X-ray θ-2θ scans revealed that the films are single-phase perovskite and highly (00l) textured. The wavelength dependence of the transmittance of the films was determined. We obtained an average transmittance of 75% in the wavelength range of 400-1100 nm and the band gap E_g=3.55 eV. The optical waveguiding properties of the films were characterized by using prism-coupling method. The distinct m lines of the guided transverse magnetic (TM) and transverse electric (TE) modes of the BTN films waveguide have been observed. The cross sectional morphology of the film was studied by scanning electron microscopy (SEM).     

Piezoelectric properties enhanced of Sr0.6(BiNa)0.2Bi2Nb2O9 ceramic by (LiCe) modification with charge neutrality

Aurivillius-type ceramics, Sr_0.6−x(LiCe)_x/2.5(BiNa)_0.2Bi₂Nb₂O₉(SLCBNBNO) with the charge neutrality, were synthesized by using conventional solid-state processing. Phase analysis was performed by X-ray diffraction analyses (XRD) and Raman spectroscopy. Microstructural morphology was assessed by the scanning electron microscopy (SEM). Structural, dielectric, piezoelectric, ferroelectric, and electromechanical properties of the SLCBNBNO ceramics were investigated. Piezoelectric properties were significantly enhanced compared to Sr_0.6(BiNa)_0.2Bi₂Nb₂O₉ (SBNBN) ceramic and the maximum of piezoelectric coefficient d₃₃ of the SBNBN-LC6 ceramic was 32 pC/N with higher Curie temperature (T_c ∼590 °C). In addition, mechanisms for the piezoelectric properties enhanced of the SBNBN-based ceramics were discussed.     

Effect of processing on the properties of Bi3.15Nd0.85Ti3O12 thin films

Various crystallization parameters were studied during the fabrication of Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT) thin films on Pt/Ti/SiO₂/Si (100) by metal organic solution decomposition method. The effect of crystallization processes, crystallization ambients on the properties of BNdT thin films such as orientation, ferroelectric properties were examined. By adopting different fabrication processes, it is possible to get both highly c-axis oriented as well as randomly oriented thin films. Highly c-axis oriented BNdT thin film showed a large remnant polarization (2P_r) of 70 μC/cm² at an applied voltage of 10 V and exhibited a fatigue free behavior unto 2 × 10⁹ switching cycles. The improved ferroelectric properties of BNdT thin films suggest their suitability for high density ferroelectric random access memory applications.     

New substitutions and novel derivatives of the Aurivillius phases, Bi5TiNbWO15 and Bi4Ti3O12

We investigated isomorphous substitution of several metal atoms in the Aurivillius structures, Bi₅TiNbWO₁₅ and Bi₄Ti₃O₁₂, in an effort to understand structure-property correlations. Our investigations have led to the synthesis of new derivatives, Bi₄LnTiMWO₁₅ (Ln = La, Pr; M = Nb, Ta), as well as Bi₄PbNb₂WO₁₅ and Bi₃LaPbNb₂WO₁₅, that largely retain the Aurivillius (n = 1) + (n = 2) intergrowth structure of the parent oxide Bi₅TiNbWO₁₅, but characteristically tend toward a centrosymmetric/tetragonal structure for the Ln-substituted derivatives. On the other hand, coupled substitution, 2Ti^IV → M^V + Fe^III in Bi₄Ti₃O₁₂, yields new Aurivillius phases, Bi₄Ti_3−2xNb_xFe_xO₁₂ (x = 0.25, 0.50) and Bi₄Ti_3−2xTa_xFe_xO₁₂ (x = 0.25) that retain the orthorhombic noncentrosymmetric structure of the parent Bi₄Ti₃O₁₂. Two new members of this family, Bi₂Sr₂Nb₂RuO₁₂ and Bi₂SrNaNb₂RuO₁₂ that are analogous to Bi₂Sr₂Nb₂TiO₁₂, possessing tetragonal (I4/mmm) Aurivillius structure have also been synthesized.     

Structure study of Bi4Ti3O12 produced via mechanochemically assisted synthesis

Nanosized bismuth titanate was prepared via high-energy ball milling process through mechanically assisted synthesis directly from their oxide mixture of Bi₂O₃ and TiO₂. Only Bi₄Ti₃O₁₂ phase was formed after 3 h of milling time. The excess of 3 wt% Bi₂O₃ added in the initial mixture before milling does not improve significantly the formation of Bi₄Ti₃O₁₂ phase comparing to stoichiometric mixture. The formed phase was amorphized independently of the milling time. The Rietveld analysis was adopted to determine the crystal structure symmetry, amount of amorphous phase, crystallite size and microstrains. With increasing the milling time from 3 to 12 h, the particle size of formed Bi₄Ti₃O₁₂ did not reduced significantly. That was confirmed by SEM and TEM analysis. The particle size was less than 20 nm and show strong tendency to agglomeration. The electron diffraction pattern indicates that Bi₄Ti₃O₁₂ crystalline powder is embedded in an amorphous phase of bismuth titanate. Phase composition and atom ratio in BIT ceramics were determined by X-ray diffraction and EDS analysis.     

Size effects of polycrystalline lanthanum modified Bi4Ti3O12 thin films

The film thickness dependence on the ferroelectric properties of lanthanum modified bismuth titanate Bi_3.25La_0.75Ti₃O₁₂ was investigated. Films with thicknesses ranging from 230 to 404 nm were grown on platinum-coated silicon substrates by the polymeric precursor method. The internal strain is strongly influenced by the film thickness. The morphology of the film changes as the number of layers increases indicating a thickness dependent grain size. The leakage current, remanent polarization and drive voltage were also affected by the film thickness.     

Piezoelectric properties of Bi4Ti3O12 thin films annealed in different atmospheres

Bismuth titanate (Bi₄Ti₃O₁₂—BIT) films were evaluated for use as lead-free piezoelectric thin-films in micro-electromechanical systems. The films were grown by the polymeric precursor method on Pt/Ti/SiO₂/Si (1 0 0) (Pt) bottom electrodes at 700 °C for 2 h in static air and oxygen atmospheres. The domain structure was investigated by piezoresponse force microscopy (PFM). Annealing in static air leads to better ferroelectric properties, higher remanent polarization, lower drive voltages and higher piezoelectric coefficient. On the other hand, oxygen atmosphere favors the imprint phenomenon and reduces the piezoelectric coefficient dramatically. Impedance data, represented by means of Nyquist diagrams, show a dramatic increase in the resistivity for the films annealed in static air atmopshere.     

Effects of substrate temperature on Bi0.8La0.2FeO3 thin films prepared by pulsed laser deposition

Bi_0.8La_0.2FeO₃ thin films on Pt/TiO₂/SiO₂/Si substrates at various substrate temperatures from 500 °C to 750 °C are prepared by pulsed laser deposition, and their microstructures and ferroelectric/magnetic properties are carefully investigated using various techniques. It is observed that the crystallographic orientation and Fe-ion valence state depend significantly on the substrate temperature, which consequently influences considerably on the ferroelectric and magnetic properties of the thin films. A considerable improvement of the ferroelectric and magnetic properties of the thin films can be achieved by optimizing the substrate temperature for deposition.     

Integration of stacked capacitor module with ultra-thin ferroelectric SrBi2Ta2O9 film for high density ferroelectric random access memory applications at low voltage operation

The crystallization route of thin SrBi₂Ta₂O₉ (SBT) films deposited on Pt(100 nm)/Ti(10 nm)/SiO₂/Si substrate is investigated at different annealing temperatures by atomic force microscopy (AFM) and X-ray diffractometry (XRD). To evaluate the SBT film properties for low voltage operation and for high storage density (>16 MBit), SBT is deposited at different film thicknesses. Furthermore, the performance of a Pt/SBT/Pt capacitor on a barrier-/contact-layer/polysilicon-plug architecture suitable for stacked capacitor memories is investigated by transmission electron microscopy (TEM)/energy dispersive X-ray analysis (EDX) and electrical measurements. It is shown that an oxidized and highly resistive contact layer can be recovered by electrical pulses. Finally, a process solution for a successful integration of 38 nm thin SBT films into this structure is provided.     

Bi4LnNb3O15 (Ln = La, Pr, Nd) and Bi4LaTa3O15: New intergrowth Aurivillius related phases

We describe the synthesis and characterization of new intergrowth Aurivillius related phases, Bi₄LnNb₃O₁₅ (Ln = La, Pr, Nd) and Bi₄LaTa₃O₁₅. Both powder X-ray diffraction and electron microscopy investigations show that the compounds adopt orthorhombic structures with the cell parameters a ∼ 5.5 Å, b ∼ 5.5 Å and c ∼ 20.9 Å, suggesting an ordered intergrowth structure that consists of n = 1 [Bi₂NbO₆]⁻ and n = 2 [Bi₂LnNb₂O₉]⁺ Aurivillius fragments which are stacked alternately along the c-axis. The oxides do not show a second harmonic generation (SHG) response toward 1064 nm laser radiation; they do not show a ferroelectric-paraelectric transition either between 30 and 900 °C in dielectric measurements, indicating a centrosymmetric structure. Optical absorption studies show that the intergrowth phases possess considerably smaller band gaps than the parent Nb₂O₅ and Ta₂O₅.     

Ag/Bi3.25La0.75Ti3O12/Bi4Ti3O12/Si结构铁电薄膜制备及其铁电性能的研究

利用溶胶-凝胶(sol-gel)方法,在硅基底上制备了Bi3.25La0.75Ti3O12/Bi4Ti3O12/Si铁电薄膜,其中Bi4Ti3O12作为缓冲层.用XRD方法分析了该结构铁电薄膜的物相结构;用扫描电镜对薄膜样品进行表面形貌观察;并且对该结构的铁电性能进行了研究.     

Magnetic field induced ferroelectric and dielectric properties in Pb(Zr0.5Ti0.5)O3 films containing Fe3O4 nanoparticles

About 1.05 µm-thick Pb(Zr_0.5Ti_0.5)O₃ (PZT) films containing Fe₃O₄ nanoparticles were deposited on LaNiO₃-coated silicon substrates through a sol-gel technique. Fe₃O₄ nanoparticles were effectively dispersed into PZT solution under the involvement of polyvinylpyrrolidone. X-ray diffraction confirmed the coexistence of PZT and Fe₃O₄ phases without other impurity phases. Scanning electron microscope revealed that the thick composite films possess well-defined and crack-free microstructure. The composite films exhibit good ferroelectric and ferromagnetic properties at room temperature. An obvious magnetodielectric effect has been demonstrated in the Pb(Zr_0.5Ti_0.5)O₃/Fe₃O₄ composite films. Magnetic field induced change in ferroelectric polarization loop may support the possible magnetoelectric coupling between PZT and Fe₃O₄ phases.     

Electric and magnetic properties of Pb(Zr0.52Ti0.48)O3-CoFe2O4 particle composite thin film on the SrTiO3 substrate

We deposited a thin epitaxial Pb(Zr_0.52Ti_0.48)O₃ (PZT) layer on the (0 0 1) SrTiO₃ (STO) substrate doped with Nb (0.5 wt.%), then grew composite thin film of CoFe₂O₄ (CFO) and PZT phases on it. X-ray diffraction and high resolution transmission electron microscopy showed that the PZT and CFO phases in the film had perfect epitaxial structures. CFO nanoparticles were embedded in PZT matrix randomly, which was useful to enhance the insulativity of the composite film. The composite thin film exhibited good ferromagnetic and ferroelectric properties. The dielectric constants of the composite thin film kept unchangeable in a wide bias electric field, but increased in a magnetic field, namely, magnetodielectric effect. The possible reasons for the magnetodielectric effect were discussed.     

Ferroelectric phase transition in Ba4SrSmTi3V7O30 ceramics

Polycrystalline Ba₄SrSmTi₃V₇O₃₀ sample was prepared using high-temperature solid-state reaction technique. Preliminary X-ray structural analysis of the compound shows the formation of a single phase compound (orthorhombic crystal system) at room temperature. Microstructures of the compound exhibit uniform distribution of grains over the surface of the sample. Detailed studies of dielectric and electrical properties as a function of frequency (1 kHz to 1 MHz) and temperature (31 °C to 475 °C) show that, the compound exhibits a diffuse ferroelectric phase transition. Measurements of electrical conductivity (ac) as a function of temperature suggest that the compound has semiconducting properties much above the room temperature with a negative temperature coefficient of resistance behavior. The existence of ferroelectricity was confirmed from polarization studies.     

Nanoscale leakage current measurements in metal organic chemical vapor deposition crystalline SrTiO3 films

The properties of SrTiO₃ thin films, grown by liquid injection metal organic chemical vapor deposition on Si/SiO₂, using a mixture of precursors, have been investigated at the nanoscale using an Atomic Force Microscope in the so-called Conductive Atomic Force Microscopy mode. Maps of the leakage currents with a nanometric resolution have been obtained on films elaborated at different temperatures and stoichiometries in order to discriminate the role of each parameter on the onset of leakage currents in the resulting layers. It appears that the higher the deposition temperature, the higher the leakage currents of the films. The mapping with a nanometric precision allows to show a heterogeneous behaviour of the surface with leaky grains and insulating boundaries. The study of films elaborated at the same temperature with different compositions supports the assumption that the leakage currents on Ti-rich layers are far higher than on Sr-rich layers.     

钛酸铋陶瓷及其电性能的研究

采用NaCl-KCl熔盐法合成出片状钛酸铋粉体,并制备了钛酸铋陶瓷.对所得陶瓷进行了相结构与显微组织及电性能的研究,结果表明,粉体烧结后为纯钙钛矿型钛酸铋陶瓷,微观形貌呈片状,并且随粉体合成时所用熔盐含量的增加,陶瓷晶粒的片状尺寸不断增大,其介电常数先减小,后增加,熔盐为5%(质量分数)时合成的粉体烧结成瓷后,其介电常数具有最小值,同时电阻率则随着合成粉体时所用熔盐含量的增加不断增加.     

Z-scan measurement for the nonlinear absorption of Bi2.55La0.45TiNbO9 thin films

Bi_2.55La_0.45TiNbO₉ (BLTN-0.45) thin films with layered aurivillius structure were fabricated on fused silica substrates by pulsed laser deposition technique. Their structure, fundamental optical constants, and nonlinear absorption characteristics have been studied. The film exhibits a high transmittance (> 60%) in visible-infrared region. The optical band gap energy was found to be 3.44 eV. The optical constant and thickness of the films were characterized using spectroscopic ellipsometric (SE) method. The nonlinear optical absorption properties of the films were investigated by the single-beam Z-scan method at a wavelength of 800 nm laser with a duration of 80 fs. We obtained the nonlinear absorption coefficient β = 4.64 × 10^− 8 m/W. The results show that the BLTN-0.45 thin film is a promising material for applications in absorbing-type optical device.