R. E. Melgarejo

Large ferroelectric response in Bi4−xNdxTi3O12 films prepared by sol–gel process

Neodymium-substituted Bi4Ti3O12 (i.e., Bi4−xNdxTi3O12) were synthesized by sol–gel process for different compositions. Thin films were deposited on Pt (i.e., Pt/TiO2/SiO2/Si) substrate by spin coating. Materials were characterized by x-ray diffraction and Raman spectroscopy. This study indicates that the material makes a solid solution for the compositions: x=0.00, 0.26, 0.46, 0.75, 0.85, 1.00, and 2.00, where an Nd ion replaces the Bi site. The prominent effect of Nd substitution is observed in low-frequency Raman modes. Sol–gel derived thin films of Bi3.54Nd0.46Ti3O12 on a Pt substrate and postannealed at 700 ° C were tested for ferroelectric response which showed high remnant polarization (Pr=25 μC/cm2).

Synthesis and Characterization of Sr1− xBa xBi2Ta2O9 Materials

Due to its endurance to ferroelectric fatigue, SrBi 2 Ta 2 O 9 (SBT) has been extensively investigated. We report here the synthesis of Sr 1− x Ba x Bi 2 Ta 2 O 9 ( x = 0.0, 0.1, 0.5, 1.0) using a solution-based route. The precursors used in this work were the salts of strontium, barium, bismuth, and tantalum ethoxide. X-ray diffraction and Raman spectroscopic studies indicated the formation of complete solid solution system for Sr 1− x Ba x Bi 2 Ta 2 O 9 . This material system may provide interesting properties relevant to microwave tuning and ferroelectric memory applications, which are under investigation.

Synthesis and Structural Characterization of BiFeO3–BaTiO3 Materials

BiFeO 3 material shows simultaneous ferromagnetic and ferroelectric behavior, therefore their is research interest in such materials for novel bi-functional devices. The partial substitution of Ba and Ti ions at Bi and Fe sites may affect the functional properties of the parent BiFeO 3 material. Substituted BiFeO 3 material with similar type of materials such as BaTiO 3 and Bi 4−x Nd x Ti 3 O 12 were synthesized and characterized by x-ray diffraction and Raman spectroscopy. Single phase thin films is achieved solution route for the composition x < 0.5. The BiFeO3 films showed weak ferroelectric polarization P r = 2.2 μC/cm 2 and BiFeO 3 —Bi 3.44 Nd 0.56 Ti 3 O 12 films also showed improved ferroelectric polarization P r = 10 μm/cm 2 good saturation field.

Structural Characterization of [(1-x) SrBi 2 Nb 2 O 9 − (x) Bi 3 TiNbO 9 ] for Ferroelectric Applications

Bismuth-layered-structure materials with (Bi 2 O 2 ) 2+ layers intervening with pseudo perovskite blocks (M n m 1 R n O 3n+1 ) 2 m , where n = 1,2,3,4,5, M is mono, di, or trivalent ions such as Ba, Sr, Bi, Pb; R is tetra, penta-, or hexavalent ions such as Ti, Ta, Nb, show interesting ferroelectric and dielectric properties. Aurivillius phase [(1-x) SrBi 2 Nb 2 O 9 m (x) Bi 3 TiNbO 9 ] family of material has been synthesized by a chemical solution method, and thin films were deposited by spin coating. The samples were characterized by x-ray diffraction, Raman spectroscopy and scanning electron microscopy. The study reveals that a complete solid solution is formed for all compositions. Thin films deposited on ITO coated polished stainless steel substrate showed ferroelectric response.

Growth and properties of Sr1−xBaxBi2TaNbO9 materials and thin films

Sr1−xBaxBi2TaNbO9 materials have been synthesized using a chemical solution route. Detailed x-ray diffraction and Raman spectroscopic studies indicates the formation of complete solid solutions for all compositions (x = 0.0 to 1.00) in Sr1−xBaxBi2TaNbO9. Thin films were deposited by spin coating. Optical transmission of the film deposited on quartz disk showed the typical interference effect of optical thin films. Ferroelectric polarization on Sr0.5Ba05Bi2TaNbO9 film deposited on Pt substrate and annealed at 700 °C, was measured to be 13.5 μC/cm2.

Structural and electrical properties of Sr1-xBaxBi2Ta2O9 thin films

Bismuth-based layered and perovskite tantalates, titanates and niobates have received special attention as ferroelectric and dielectric materials. Sr 1-x Ba x Bi 2 Ta 2 O 9 (x = 0.0, 0.2, 0.5, 0.7, and 1) were synthesized using a chemical solution route. As revealed by X-ray diffraction studies, they make a complete solid solution for all values of x. Thin films were deposited by spin coating. Stoichiometric thin films were achieved on quartz and stainless steel substrates at a process temperature below 700°C. Films were also characterized by Raman and impedance spectroscopy. The ferroelectric memory has been measured with Pr 27 μm/cm 2 on the Sr 0.3 Ba 0.7 Bi 2 Ta 2 O 9 film deposited on a stainless steel substrate and annealed at 650°C.

Ferroelectric Behavior of Sol-Gel Derived Bi4-xNdxTi3O12 Thin Films

Rare earth substituted bismuth titanates are important materials for ferroelectric and microwave applications. Bi4-xNdxTi3O12 materials were synthesized for different compositions by sol-gel process and thin films were deposited on Pt (Pt/TiO2/SiO2/Si) substrate by spin coating. X-ray and Raman spectroscopic studies of the films annealed at 700°C indicates a complete solid solution for the compositions x < 1. Ferroelectric response seems to differ with film composition and thickness. The 0.50 μm thick Bi3.44Nd0.56Ti3O12 film showed a ferroelectric polarization Pr = 58 μC/cm2 and fatigue free behavior. Large polarization is attributed to the dipole formation which may tilt TiO4 octahedra to Bi2O2 interlayer of the unit cell.

Studies of Bi 4−x Gd x Ti 3 O 12 Bifunctional Material

Gadolinium-substituted Bi 4 Ti 3 O 12 (i.e. Bi 4−x Gd x Ti 3 O 12 ) were synthesized by sol-gel process for different compositions, and thin films were deposited on Pt (Pt/TiO 2 /SiO 2 /Si) substrate by spin coating. Post annealed films at 700° C were investigated for their structural properties using x-ray diffraction and Raman spectroscopy indicating solid solution for compositions: x = 0.00, 0.46, 0.56, and 0.85 where Bi ion is replaced by Gd-ion. Sol-gel derived Pt/Bi 4−x Gd x Ti 3 O 12 film/Pt capacitor structure was tested for dielectric, ferroelectric, and leakage current responses. Films showed ferroelectricity with polarization, P r = 22 µC/cm 2 for composition: x = 0.46. Magnetic response of the powder sample for composition: x = 0.85 was tested using SQUID, which showed superparamagnetic at room temperature and magnetic at 5 K with magnetic coercivity (Hc) = 29 Oe and very small remanance (σ r ) = 5.4 × 10 −4 emu/g.

Rare earth substituted Bi4Ti3O12 thin films with large ferroelectric response

Rare earth substituted Bi4Ti3O12, such as, Bi4−x Nd x Ti3O12 (BNT) are important materials for ferroelectric memory devices. BNT materials at different concentration of Nd substitution were synthesized by sol-gel process, and thin films were deposited on Pt (i.e. Pt/TiO2/SiO2/Si) substrate by spin coating. Structural properties of the films were examined by x-ray and Raman spectroscopy, which shows a complete solid solution for the compositions x < 0.85. Ferroelectric response was measured for various film compositions. The 0.65 μm thick Bi3.44Nd0.56Ti3O12 (BNT56) film showed a ferroelectric polarization P r = 70 μC/cm2 ( 2 P r = 140 μC/cm2). Exceptionally large polarization in Bi3.44Nd0.56Ti3O12 film is attributed to the suppression of c-axis growth by with improved diffusion controlled processing of the films, and the dipole formation which tilts TiO6 tetrahedron to Bi2O2 interlayer of the unit cell.

Synthesis and Ferroelectric Response of Bi 4−x Nd x Ti 3 O 12 Thin Films

Nd doped Bi 4 Ti 3 O 12 layered materials were synthesized using a solution chemistry route. Thin films were deposited by spin coating. Powder and thin film samples were characterized by x-ray diffraction and Raman spectroscopy. Ferroelectric response of Bi 4 m x Nd x Ti 3 O 12 thin film (x = 0.95), deposited on Pt substrate is reported.