Water–based synthesis of La0,5Sr0,5CoO3 (LSCO) electrodes for ferroelectric thin films

Abstract

La_0,5Sr_0,5CoO₃ (LSCO) thin films were prepared from water solutions of lanthanum nitrate La(NO₃)₃x6H₂O, strontium nitrate Sr(NO₃)₂ and cobalt nitrate Co(NO₃)₂x6H₂O with different amounts of polyvinylalcohol (PVA). Thin films were deposited on platinum coated and thermally oxidized silicon substrates. The influence of the amount of PVA on the thermal decomposition of LSCO precursors, the surface wetting and the microstructure of LSCO thin films were investigated. The effort was also focused on the optimization of the thermal treatment to obtain dense LSCO thin films.     

The Study of Ferroelectric La-Doped PbTiO3 Thin Films Prepared by RF Magnetron Sputtering

Ferroelectric La-modified lead titanate (PLT) thin film were grown on Pt/Ti/SiO2/Si by sputtering the Pb_0.93La_0.07TiO₃ targets containing an amounts of excess 8% PbO. The effects of sputtering and annealing conditions on the crystalline structures and the surface morphologies of the PLT thin films have been investigated. The remanent polarization (Pr) and the coercive field of the PLT film through rapid thermal annealing (RTA) was 10.2 μC/cm² and 45 kV/cm respectively. The maximum pyroelectric coefficient reached 19 nC/cm².K at 20°C.     

Defect Chemistry of Y Doped BaTiO3

Defect chemistry of Y doped BaTiO₃ was investigated as a function of the Ba/Ti ratio. When the Ba/Ti ratio was greater than unity, Y^{3 +} was substituted for the normal Ti site and the equilibrium conductivity showed a strong evidence of acceptor-doped behavior. With the Ba/Ti ratio < 1, Y^{3 +} was substituted for the Ba site and the equilibrium conductivity showed donor-doped behavior. In the case excess Y₂O₃ was added to the stoichiometric BaTiO₃(Ba/Ti = 1), the conductivity profile showed a donor-doped behavior at low concentrations (< 1.0 mol%), whereas, at higher donor levels (> 2.0 mol%), the equilibrium conductivity minimum shifted toward lower Po₂, indicating acceptor doped behavior.     

Composition measurement of paraelectric SrTiO3 layer

Abstract

Since composition is an important parameter affecting the dielectric properties in paraelectric SrTiO₃ layers, composition is determined by Rutherford backscattering spectrometry (RBS) measurement. In this measurement, specifically for achieving precise composition measurement, the RBS spectra of Sr, Ti and O must be separated individually. This spectrum separation can only be attained when thin (800 A[ddot] thick) Sr_xTiO_y layers are deposited on graphite substrate. The measurement is performed for layers deposited at different O₂ partial pressure ratios and sputtering pressures. This measurement indicates that composition of O, y, in Sr_xTiO_y layer decreases from 3.7 to 2.7 with the decrease of O₂ partial pressure raito, R(=O₂/O₂ + Ar) from 1.0 to 0.83. Composition of Sr, x, also changes from 1.1 to 0.6 with this change. With the decrease of sputtering pressure from 10 to 5 mTorr, however, composition, y, is held at 2.7 and only the composition, x, increases from 0.6 to 1.1. This composition measurement is useful for the deposition of optimized dielectric layer employed in the charge storage capacitor.     

Glycolate tantalum based solutions for the sol-gel spin-coating deposition of SrBi2Ta2O9 thin films

Abstract

The reaction of tantalum ethoxide with a glycol solvent produces the interchange of the ethoxide groups with the glycol. As a result, a polymeric derivative is formed with a high resistance towards hydrolysis. Compounds of Sr(II) and Bi(II) can be added to this Ta-glycol sol, leading to strontium bismuth tantalate (SBT) precursor solutions stable in air. These solutions were spin-coated onto two substrates: Pt/TiO₂/SiO₂/(100)Si and Ti/Pt/Ti/SiO₂/(100)Si. Crystallisation of the SBT phase was carried out by a first formation of a fluorite phase that evolves to the layered perovskite at temperatures over 600°C. During crystallisation, a larger tendency to the formation of a substrate/film interface was observed in the films deposited onto Ti/Pt/Ti/SiO₂/(100)Si than onto Pt/TiO₂/SiO₂/(100)Si. A remanent polarisation of P_r5 μC/cm² and a coercive field of E_c <100 kV/cm were measured in the films on Pt/TiO₂/SiO₂/(100)Si. These films retain its remanent polarisation, P_r, up to 10⁵seconds and are fatigue-free up to 10⁹ cycles.     

The effect of Co addition on the electrical conductivity of Sr- and Mg-doped LaAlO3

Co was added to see its effect on the electrical conductivity of Sr- and Mg-doped LaAlO₃ (La_0.9Sr_0.1 Al_0.9Mg_0.1O₃, LSAM). Electrical conductivities of La_0.9Sr_0.1(Al_0.9Mg_0.1)_{1− x}Co_xO₃ (LSAMC) for x = 0–0.20 were measured using 2-probe a.c. and 4-probe d.c. method at temperature between 300 and 1300^∘C in air, and as a function of Po ₂ (1–10⁻¹⁵ atm) at 1200^∘C. Electrical conductivities in air increased with increasing Co content, while their activation energy decreased. From the impedance spectroscopy analysis, it was found that both the grain and the grain boundary conductivities of LSAMC samples increased rapidly with Co-addition. LSAMC samples were oxygen ion conductors in low Po₂ and mixed conductors in high Po ₂ up to x = 0.1 just like LSAM. With Co-doping, p-type conductivities increased, however, ionic conductivities remained nearly constant.     

P-Type Partial Conductivity of Donor(La)-Doped BaTiO3

P-type partial conductivity has been determined on donor (La _Ba )-doped BaTiO₃ in full thermodynamic equilibrium state at a fixed temperature of 1200°C: For the nominal compositions of Ba_0.99La_0.01Ti_0.9975O₃, Ba_0.99La_0.01TiO₃ and Ba_0.985La_0.01TiO₃, the p-type conductivity is found to vary with oxygen activity as _p = (_m/2)(a _{O 2}/a _{O 2}*)^+1/4 with _m 0.01 S cm^–1 and a _{O 2}* 32, 120, 310, respectively, in the a _{O 2} region where conventionally the electronic conductivity varies as a_{O 2} ^–1/4 and hence, the doped donors are believed to be compensated by cation vacancies (say, [La_Ba ] 4[VPrime;_Ti]). This experimental fact supports that in the vicinity of the stoichiometric composition of the system which falls approximately at a _{O 2} = a _{O 2}*, while cation vacancy concentration is fixed by the donor concentration, oxygen vacancy concentration in the minority is also essentially fixed, thus, keeping the activity of TiO₂ (or BaO) fixed. It is consequently suggested that donor-doped BaTiO₃ contains a second phase even in its stoichiometric regime.     

Control of Microwave Dielectric Properties in the System BaO ⋅ Nd<Subscript>2</Subscript>O<Subscript>3</Subscript> ⋅ 4TiO<Subscript>2</Subscript>—BaO ⋅ Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ⋅ 4TiO<Subscript>2</Subscript>

BaO ⋅ Nd₂O₃ ⋅ 4TiO₂—based ceramics were prepared by the mixed oxide route. Specimens were sintered at temperatures in the range 1200–1450^∘C. Microstructures were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM); microwave dielectric properties were determined at 3 GHz by the Hakki and Coleman method. Product densities were at least 95% theoretical. The addition of up to 1 wt% Al₂O₃ to the starting mixtures reduced the sintering temperatures by at least 100^∘C. Incorporation of small levels of Al into the structure (initially Ti sites) led to an increase in Q × f values, from 6200 to 7000 GHz, a decrease in relative permittivity (ε_r) from 88 to 78, and moved the temperature coefficient of resonant frequency (τ_f) towards zero. The addition of 0.5 wt% Al₂O₃ with 8 wt% Bi₂O₃ improved densification, increased both ε_r (to 88) and Q× f (to 8000 GHz) and moved τ_f closer to zero. Ceramics in the system (1 − x)BaO ⋅ Nd₂O₃ ⋅ 4TiO₂ + xBaO ⋅ Al₂O₃ ⋅ 4TiO₂ exhibited very limited solid solubility. The end member BaO ⋅ Al₂O₃ ⋅ 4TiO₂ was tetragonal in structure with the following dielectric properties: ε_r = 35; Q× f = 5000 GHz; τ_f = −15ppm/^∘C. Microstructures of the mixed Nd-Al compositions contained two distinct phases, Nd-rich needle-like grains and large Al-rich, lath-shaped grains. Products with near zero τ_f were achieved at compositions of approximately 0.14BaO ⋅ Nd₂O₃ ⋅ 4TiO₂ + 0.86BaO ⋅ Al₂O₃ ⋅ 4TiO₂, where Q× f = 8200 GHz and ε_r = 71.     

Dielectric Properties and Sintering Characteristics of CaTiO<Subscript>3</Subscript>-(Li<Subscript>1/2</Subscript>Nd<Subscript>1/2</Subscript>)TiO<Subscript>3</Subscript> Ceramics

The dielectric properties and the sintering effect upon microstructure of (1–x) CaTiO₃-x(Li_1/2Nd_1/2)-TiO₃ Ceramics are investigated in this paper. Nd³⁺ and Mg^{2 +} ions co-substitution for Ca^{2 +} on A site improves the sintering characteristic of CaTiO₃ ceramics with forming orthorhombic perovskite structure. The structure of (1 – x) CaTiO₃-x(Li_1/2Nd_1/2)TiO₃ changes from orthorhombic to tetragonal as (Li_1/2Nd_1/2)TiO₃ addition increasing. Limited solubility of (Li_1/2Nd_1/2)TiO₃ in CaTiO₃ forming a part solid solution compound achieves the adjustment of for CaTiO₃ at low sintering temperature. The proper dielectric properties with = 78, tan = 0.0006, = +7 ppm/C are obtained for 0.8Ca_0.67(Nd,Mg)_0.22TiO₃-0.2(Li_1/2Nd_1/2)TiO₃ ceramics.     

THE ELECTRICAL AND STRUCTURAL PROPERTIES OF Li2CO3 DOPED 0.7(Ba,Sr)TiO3-0.3MgO CERAMICS

ABSTRACT

We have studied the formation and characterization of Li₂CO₃ doped 0.7(Ba,Sr)TiO₃-0.3MgO ceramics for the low temperature sintering and microwave applications. In this study 1 ～ 5 wt% of Li₂CO₃ was added to the 0.7(Ba,Sr)TiO₃-0.3MgO ceramic materials to reduce the sintering temperature. The MgO contents, which added in this experiment, play a role of improving dielectric permittivity such as low frequency dispersion and low loss tangent.

In this paper, we will discuss the crystalline properties, dielectric properties, and the microstructures of Li₂CO₃ doped 0.7(Ba,Sr)TiO₃- 0.3MgO ceramics. No pyro phase was observed in the X-ray diffraction method. Very weak frequency dispersion of dielectric permittivity was observed from the 1 kHz to 1 MHz range. Different grain sizes of Li₂CO₃ doped 0.7(Ba_0.5Sr_0.5)TiO₃-0.3MgO ceramics were observed through the SEM methods.     

Synthesis and Characterization of Zn-Doped TiO2 Nanoparticles via Sonochemical Method

Zn-doped TiO₂ nanoparticles were successfully fabricated using sonochemical method accompanying post calcination process. Titanium isopropoxide (Ti[OC₃H₇]₄) and Zinc chloride (ZnCl₂) were used as starting precursors for Ti and Zn sources, respectively. The homogeneous mixing solution of different Zn (0–1 mol%) and Ti ratio were irradiated in high intensity ultrasound sonometer (750 W 20 kHz) for 30 min at room temperature to obtain as-synthesized Zn-doped TiO₂ nanoparticles followed by calcination at 400–700°C. To evaluate the structure and phase identification of prepared powders, the X-ray diffraction (XRD) and Raman spectroscopy were employed. The results reveal that the as-synthesized Zn-doped TiO₂ nanoparticles are in anatase phase and their crystallinity increases with increasing calcined temperature. The morphology of as-synthesized powders was investigated by transmission electron microscope (TEM). The effect of Zn content and calcinations temperature on TiO₂ properties was also discussed.     

Epitaxial Pb(Zr,Ti)O<Subscript>3</Subscript> Capacitors on Si by Liquid Delivery Metalorganic Chemical Vapor Deposition

La_0.5Sr_0.5CoO₃/Pb(Zr_xTi_1–x)O₃/La_0.5Sr_0.5CoO₃ capacitors have been successfully fabricated by liquid delivery metalorganic chemical vapor deposition on Si wafers using SrTiO₃ thin layer (20 nm) as a template. Zr(dmhd)₄ in tetrahydrofuran was used as Zr precursor for compatible thermal behavior with Pb(thd)₂ and Ti(OiPr)₂(thd)₂ precursors. The dependence of the ferroelectric film composition on the precursor mixing ratio and growth temperature has been systematically studied by Rutherford Backscattering (RBS). Ferroelectric and piezoelectric properties at the composition close to morphotropic phase boundary region (Pb(Zr_0.5Ti_0.5)O₃) have been investigated for application in nonvolatile ferroelectric random access memories and microelectromechanical system (MEMS). These capacitors show desirable ferroelectric properties, which proves that this approach is very promising for both fundamental study and potential applications. The changes of spontaneous polarization (P_s) and piezoelectric coefficient (d₃₃) with Ti/(Zr + Ti) ratio are also presented and compared with theoretical values.     

Site Preference of La in Bi<Subscript>3.75</Subscript>La<Subscript>0.25</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Using Neutron Powder Diffraction and Raman Scattering

Both structural refinement using neutron powder diffraction data and Raman scattering were carried out to determine the site preference of La atoms and the cation distribution in Bi_3.75La_0.25Ti₃O₁₂ compound. Of three possible cation-disorder models, the best structural refinement result was obtained from a model that La atoms substitute only for Bi atoms outside of the TiO₆ octahedra in the Bi₂Ti₃O₁₀ unit. The model proposed by the structural refinement was corroborated by the Raman spectroscopic study. The final weighted R-factor, R_wp, and the goodness-of-fit indicator, S (= R_wp/R_e), based on the neutron diffraction and the Raman scattering were 4.12% and 1.43, respectively. The occupancy of La atoms for two Bi sites in the perovskite-like unit was 0.082 and 0.074, respectively. The refined model described a structure in monoclinic space group B1a1 with Z = 4, a = 5.4387(1) Å, b = 5.4129(1) Å, c = 32.8441(1) Å and = 90.03(1).     

The Effect of La-Doped Bi4Ti3O12 Buffer Layer on Crystallinity and Ferroelectric Properties of PbZr0.58Ti0.42O3/Bi3.25La0.75Ti3O12 Multilayered Thin Films

PbZr_0.58Ti_0.42O₃ (PZT) ferroelectric thin films with Bi_3.25La_0.75Ti₃O₁₂ (BLT) buffer layer of various thickness were fabricated on Pt/TiO₂/SiO₂/p-Si(100) substrates by rf-magnetron sputtering method. The pure PZT film showed (111) preferential orientation in the XRD patterns, and the PZT/BLT films showed (110) preferential orientation with increasing thickness of the BLT layer. There were no obvious diffraction peaks for the BLT buffer layer, for its thin thickness in PZT/BLT multilayered films. There were the maximum number of largest-size grains in PZT/BLT(30 nm) film among all the samples from the surface images of FESEM. The growth direction and grain size had significant effects on ferroelectric properties of the multilayered films. The fatigue characteristics suggested that 30-nm-thick BLT was just an effective buffer layer enough to alleviate the accumulation of oxygen vacancies near the PZT/BLT interface. The comparison of these results suggests that the buffer layer with an appropriate thickness can improve the ferroelectric properties of multilayered films greatly.     

Characteristics of Bi4Ti3O12 thin films on ITO/glass and Pt/Si substrates prepared by R.F. sputtering and rapid thermal annealing

Bi₄Ti₃O₁₂ thin films are deposited on ITO/glass and Pt/Ti/Si(100) substrates by R.F. magnetron sputtering at room temperature. The films are then heated by a rapid thermal annealing (RTA) process conducted in oxygen atmosphere at temperatures ranging from 550–700^∘C. X-ray diffraction examination reveals that the crystalinity of the films grown on Pt/Ti/Si is better than that of the films grown on ITO/glass under the same fabrication conditions. SEM observation shows that the films grown on Pt/Ti/Si are denser than those grown on ITO/glass substrates. Interactive diffusion between the Bi₄Ti₃O₁₂ film and the ITO film increases with the increase of annealing temperature. The optical transmittance of the thin film annealed at 650^∘C is found to be almost 100% when the effect of the ITO film is excluded. The relative dielectric constants, leakage currents and polarization characteristics of the two films are compared and discussed.     

Structural and Multiferroic Properties of Bi3.4La0.6Ti3O12/CoFe2O4 Composite Thin Films

Bi_3.4La_0.6Ti₃O₁₂ and CoFe₂O₄ were synthesized by chemical solution route, and Bi_3.4La_0.6Ti₃O₁₂/CoFe₂O₄ multilayers were deposited by spin coating on Pt substrate. X-ray diffraction of multilayer structures reveals composite-like polycrystalline film. Leakage current is less than 10^?5 A at electric field < 90 KV/cm and follows the Ohmic behavior. Dielectric response shows relaxation and the loss (tan δ) is below 3% at 10⁶ Hz. Room temperature ferrroelectric polarization (P_r) = 20.2 μC/cm² and ferromagnetic memory (M_r) = 46.5 emu/cm³ has been obtained. Co-existence of FE and FM response can be attributed to stress and different permeability and permittivity involved in multilayer structures.     

Effect of Sb2O3 addition on the varistor characteristics of ZnO-Bi2O3-ZrO2-MtrO (Mtr = Mn, Co)

Effect of Sb₂O₃ addition on the varistor characteristics of pyrochlore-free ZnO-Bi₂O₃-ZrO₂-M_trO (M_tr = Mn, Co) system previously proposed has been studied. With Sb₂O₃ up to 0.1 mol%, a gradual enhancement of densification and the grain growth inhibition were seen in the system sintered between 900 and 1200^∘C. In X-ray diffraction patterns, small amount of pyrochlore appeared in the specimens doped with Sb₂O₃ (>0.06 mol%), which is thought responsible for the sintering behavior. Enhanced values of non linear coefficient (α) were obtained in ZnO-Bi₂O₃-ZrO₂ (ZBZ) doped with 0.001 mol% Sb₂O₃, but was leveled off at higher concentrations. In ZBZ added with M_trO (M_tr = Mn, Co), significant increase of nonlinear coefficient (α > 30) along with low leakage current (I _L ≪ 100 μA/cm²) was attained. The α-enhancement effect of Sb₂O₃, however, was not observed in high-α ZBZ added with M_trO. As for degradation, addition of a trace amount (0.001 mol%) of Sb₂O₃ to ZBZM_tr was efficient, especially in I _L.     

The fabrication,characterization of honeycomb-type porous Ag/N-TiO2 nanomaterial and its application in SERS study

ABSTRACT

Combined template method with sol-gel method to make the mixed solution including polystyrene microsphere emulsion, TiO₂ sol and NH₃·H₂O aging at room temperature. Annealing at 500 centigrade for 2 hours on mesoporous TiO₂ nano material doped with nitrogen. Wrapped Ag nanoparticles on the surface of mesoporous TiO₂ nano material through redox reaction. The morphology and optical porosities were characterized by Scanning electron microscope (SEM), X-ray diffraction (XRD), BET tester and Surface enhanced Raman scattering (SERS). The results showed this material has excellent surface enhanced Raman effect, optical absorption effect and also has a great specific surface area.     

Photocatalytic WO3/TiO2 nanoparticles working under visible light

WO₃/TiO₂ was prepared by modifying the surface of TiO₂ with clusters of crystallized WO₃. Previously, we have reported that the TiO₂ covered with the monolayer of WO₃ shows greatly enhanced photocatalytic activity under UV light in decomposing VOCs. Here we report that the WO₃/TiO₂ can also be activated by visible light in the photocatalytic decomposition of gaseous 2-propanol. The structure of WO₃/TiO₂ was examined by X-ray diffraction (XRD), TEM, UV-Visible and Raman spectra. The samples with 10 mol% of WO₃ annealed at 700^∘C provide the optimum photocatalytic efficiency in visible range. We also suggest the mechanism for the WO₃/TiO₂ working under visible light.     

Electrical properties of Ga2O3-based dielectric thin films prepared by plasma enhanced atomic layer deposition (PEALD)

Ga₂O₃ and Ga₂O₃-TiO₂ (GTO) nano-mixed thin films were prepared by plasma enhanced atomic layer deposition with an alternating supply of reactant sources, [(CH₃)₂GaNH₂]₃, Ti(N(CH₃)₂)₄ and oxygen plasma. The uniform and smooth Ga₂O₃ and GTO thin films were successfully deposited. Excellent step coverage of these films was obtained by chemisorbed chemical reactions with oxygen plasma on the surface. The dielectric constant of GTO thin film definitely increased compared to Ga₂O₃ film, and the leakage currents of GTO films were comparable to Ga₂O₃ films. The leakage current density of a 40-nm-GTO film annealed at 600^∘C was approximately 1×10⁻⁷ A/cm² up to about 600 kV/cm.