High performance distributed CPW phase shifters with etched BST thin films on Ф 3″ LaAlO3 substrates

The design, fabrication and microwave properties of distributed coplanar waveguide (CPW) phase shifters using etched Ba_0.6Sr_0.4TiO₃ (BST) thin films on Ф 3″ LaAlO₃ (100) substrates were investigated. The BST thin films employed in the circuits are deposited by RF magnetron sputtering, and then annealed at 800 °C for 30 min in air. BST thin films parallel-plate capacitors were fabricated by photolithography and etching process. At 10 kHz and 600 kV/cm electric field, the dielectric tunability, remanent polarization (2P_r) and the coercive electric field (2E_C) of BST film were 28.7%, 2.265 μC/cm² and 38.8 kV/cm, respectively. The loss tangent was 0.005 at zero electric field. The CPW phase-shifter designed was subsequently fabricated by optimum BST thin films and thickened top electrodes. At 21.3 GHz and 35 V, 360° phase shift was achieved, the insertion loss was −8.5 dB, the ?gure-of-merit (FOM) was 42.4°/dB, and the return loss was −12.1 dB.     

Crystallization Temperature Limit of (Ba,Sr)TiO<Subscript>3</Subscript> Thin Films Prepared by a Non Oxocarbonate Phase Forming CSD Route

A new chemical solution deposition (CSD) route for the fabrication of Ba_0.7Sr_0.3TiO₃ (BST) thin films has been developed which completely prevents the formation of an intermediate oxo-carbonate phase. The latter has been reported previously by several authors to be responsible for increased crystallization temperatures. Barium and strontium diaminoethoxides were synthesized starting from pure barium and strontium metal and aminoethanol. These alkoxides were found to be readily soluble in a wide range of solvents and thus were excellent candidates for the CSD process. To prepare a stable precursor solution the aminoalkoxides were dissolved in 2-butoxyethanol and then used for the deposition of BST thin films. We conclude that the minimum crystallization temperature of 600C to be independent of the formation of the oxo-carbonate phase. DTA-TGA were performed on the precursors and their solutions to study their decomposition behaviour. All films annealed at different temperatures were physically characterized by XRD, IR, and SEM. The films prepared by this route at 650C were found to have high dielectric constant and the leakage currents were comparable to BST films prepared by normal carboxylate based routes at 750C.     

Preparation and Properties of Highly Oriented Sr0.3Ba0.7Nb2O6 Thin Films by a Sol-Gel Process

We succeeded in the preparation of epitaxial or highly oriented strontium-barium niobate (Sr_0.3Ba_0.7Nb₂O₆) thin film by a sol-gel process. A homogeneous coating solution was prepared with Sr and Ba acetates and Nb(OEt)₅ as raw materials, and acetic acid and diethylene glycol monomethyl ether as solvents. Sr_0.3Ba_0.7Nb₂O₆ film sintered at 900°C on MgO(1 0 0) was oriented with c-axis perpendicular to the substrate surface. Sr_0.3Ba_0.7Nb₂O₆ film sintered at 700°C on SrTiO₃(1 0 0) was an epitaxial and oriented with c-axis in parallel to the substrate surface. Transmittance of Sr_0.3Ba_0.7Nb₂O₆ film (film thickness: 144 nm) was more than 60% at the range from 400 to 800 nm. Refractive index was 2.33 at 633 nm. Dielectric constant and dielectric loss of the Sr_0.3Ba_0.7Nb₂O₆ thin films prepared on polycrystal Pt substrates were 600 and 0.06 at room temperature and 1 kHz, respectively. The curie temperature (T_c) of polycrystalline Sr_0.3Ba_0.7Nb₂O₆ thin films was about 200°C. At room temperature and 50 kHz, remanent polarization (P_r) and coercive field (E_c) of the polycrystalline thin films were 1.79 C/cm² and 2.69 kV/cm, respectively.     

Sol-gel processing and properties of cerium doped Barium Strontium Titanate thin films

A stock solution sol-gel based method for making Barium Strontium Titanate (BST) thin films has been developed. A modified titanium alkoxide was combined with a barium and/or strontium inorganic salt in methoxyethanol and ethylene glycol to form the solution. The effect of chemistry on the stability of this BST solution is discussed. The crystallization temperature of 700–725°C for rapid thermally processed films dropped by 100°C using cerium doping. The permittivity for undoped films was 250 and doping by 3 at. % Ce increased the dielectric constant by 20%. A remanent polarization of approximately 0.5 C/cm² and coercive field of 28 kV/cm were measured for the undoped films. The leakage current densities were <10 nA/cm² at E=60 kV/cm and improved for cerium concentrations up to 3 at. %. The charge storage density was 50 fF/m² at 200 kV/cm and the DC breakdown voltage was 300 kV/cm for Ce doped films.     

Ba0.6Sr0.4TiO3/聚偏氟乙烯-聚甲基丙烯酸甲酯复合材料的制备及其介电性能

采用流延热压工艺制备Ba_0.6Sr_0.4TiO₃(BST)/聚偏氟乙烯(PVDF)?聚甲基丙烯酸甲酯(PMMA)复合薄膜,研究了PMMA含量对复合材料微观组织结构和介电性能的影响规律。结果表明,BST相能够均匀分散在聚合物基体中,归因于PMMA与PVDF良好的相容性,2种聚合物之间的界面不分明;随着PMMA含量的增加,复合材料的介电常数先降低后升高,耐击穿强度和介电可调性先增加后减少。PMMA含量(体积分数)为15%的BST/PVDF?PMMA₁₅复合材料的综合性能最佳:介电常数为23.2,介电损耗为0.07,耐击穿强度为1412 kV·cm^-1,在550 kV·cm^-1偏压场下,介电可调性为26.2%。     

Low-Temperature Synthesis of Single-Phase Barium Strontium Titanate Thin Film with a nm-Seeding Technique and Its Dielectric Properties

Dielectric barium strontium titanate (Ba_0.5Sr_0.5TiO₃, BST) thin films containing crystalline seeds of BST nanoparticles were prepared on indium titanium oxide (ITO) glass electrodes with a complex alkoxide precursor method. BST precursor solution that dispersed the BST particles was spin-coated on the electrode and annealed at various temperatures. Thickness of the film was about 300 nm, and BST particle concentration in the film was varied from 0 to 17 mol%. An unseeded BST film was crystallized into a perovskite structure by annealing at 600C, while the seeding with the 17 mol%-BST particles promoted crystalline growth of BST perovskite and lowered crystallization temperature of the films to 525C. Measurement of dielectric properties at 1 kHz showed that the 4.9 mol% BST-seeded film annealed at 600C had a relative dielectric constant of 303, which was higher than that of the unseeded BST film.     

Synthesis of Free-Standing Crystalline Barium Titanate Films at Vapor/Liquid or Liquid/Liquid Interface

Synthesis of free-standing crystalline barium titanate (BaTiO₃) films at vapor/liquid or liquid/liquid interface at room temperature has been investigated. High concentration Ba, Ti alkoxides precursor solution (1.2 mol/l) or pre-hydrolyzed precursor solutions by water vapor in a H₂O/Ba molar ratio of 0 to 6 were used as dropping solutions at the interfaces. Transparent gel films were formed when partially hydrolyzed precursors (H₂O/Ba = 2 to 3) were spread out on a N₂/liquid paraffin interface. The films shrank from syneresis and vaporization of the solvent during aging at room temperature. As a result, free-standing transparent films with a thickness of around 1 m and little stoichiometric deviation were obtained by separation from the liquid surface and rinse by hexane. The films consisted of crystalline BaTiO₃ particles of less than a few nanometers. Nanostructured dense BaTiO₃ free-standing films with a grain size less than 100 nm were obtained at 1030°C.     

Synthesis,Ferroelectric and Optical Properties of (Pb,Ca)TiO3 Thin Films by Soft Solution Processing

Calcium modified lead titanate sol was synthesized using a soft solution processing, the so-called polymeric precursor method. In soft chemistry method, soluble precursors such as lead acetate trihydrate, calcium carbonate and titanium isopropoxide, as starting materials, were mixed in aqueous solution. Pb_0.7Ca_0.3TiO₃ thin films were deposited on platinum-coated silicon and quartz substrates by means of the spinning technique. The surface morphology and crystal structure, dielectric and optical properties of the thin films were investigated. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 299 and 0.065, respectively, for a thin film with 230 nm thickness annealed at 600°C for 2 h. The remanent polarization (2P_r) and coercive field (E _c) were 32 C/cm² and 100 kV/cm, respectively. Transmission spectra were recorded and from them, refractive index, extinction coefficient, and band gap energy were calculated. Thin films exhibited good optical transmissivity, and had optical direct transitions. The present study confirms the validity of the DiDomenico model for the interband transition, with a single electronic oscillator at 6.858 eV. The optical dispersion behavior of PCT thin film was found to fit well the Sellmeir dispersion equation. The band gap energy of the thin film, annealed at 600°C, was 3.56 eV. The results confirmed that soft solution processing provides an inexpensive and environmentally friendly route for the preparation of PCT thin films.     

Dielectric and tunable properties of highly (110)-oriented (Ba<Subscript>0.65</Subscript>Sr<Subscript>0.35</Subscript>)TiO<Subscript>3</Subscript> thin films deposited on Pt/LaNiO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrates

Highly (110)-oriented Ba_0.65Sr_0.35TiO₃ films were deposited on Pt/LaNiO₃/SiO₂/Si substrates by a sol–gel method. It was found that the (110)-preferred Pt film was very effective for growing (110)-oriented ferroelectric films with perovskite structure. The as-grown Ba_0.65Sr_0.35TiO₃ films showed good dielectric properties with dielectric constant and loss tangent tan δ = 0.026. Excellent dielectric tunability was also achieved in the (110)-oriented films. With applying an electric field of 230 kV/cm at 100 kHz, the dielectric tunability and the figure of merit can reach up to 63.4% and 16, respectively. These results indicate that the highly (110)-oriented Ba_0.65Sr_0.35TiO₃ film is a promising candidate for the applications in microwave tunable devices.     

Ferroelectric Thin Films of Bismuth Strontium Tantalate Prepared by Alkoxide Route

Study of the interactions in Bi(OR)3-Ta(OR)5-ROH (R = Me, Et, iPr) at 20°C show that metal ethoxides are the best of the investigated precursors for the production of bismuth tantalates via alkoxides. Polycrystalline SrBi2Ta2O9 (SBTO) and BiTaO4 films on Si-SiO2-Ti-Pt substrates with thicknesses of 0.4–0.5 m and 0.4 m, respectively, have been formed by sol-gel processing. The most stable solutions for film application were obtained by using mixed-metal Bi-Ta ethoxides and solutions of Sr carboxylate (2-ethylhexanoic acid derivative) in 2-ethylhexanoic acid. Films annealed at 700–750°C for 30 min were single-phased. SBTO films demonstrated good ferroelectric properties: remanent polarization ranged from 3.5 to 4.0 C/cm2 and coercive voltage 1.5–2.0 V, whereas BiTaO4 films showed dielectric behavior.     

Preparation of (1? x %)(Na0.5Bi0.5)TiO3– x %SrTiO3 thin films by a sol–gel method for dielectric tunable applications

(1−x%)(Na_0.5Bi_0.5)TiO₃–x%SrTiO₃ (NBTSx) thin films were deposited on Pt/TiO₂/SiO₂/Si substrates by a spin-on sol–gel method and rapid thermal annealing. The stock solutions were prepared using sodium acetate, bismuth acetate, strontium acetate, and titanium n-butoxide as precursors, ethanol, and acetic acid as solvents and acetylacetone as the chelating agent. The thermal treatment conditions were determined by thermal analyses of the dry gel powders derived from the stock solutions. Structure and dielectric tunable properties of the films were studied as functions of Sr concentration. NBTSx films exhibit the perovskite structure of a pseudo-cubic symmetry with the lattice parameters increasing with increasing Sr concentration. It was found that the substitution of Sr in Na_0.5Bi_0.5TiO₃ may greatly reduce the dielectric loss while decrease the tunability at the same time. The best figure of merit was achieved in NBTS80 films. The results were discussed and compared with related materials.     

Low-Temperature Preparation of (Ba,Sr)TiO3 Perovskite Phase by Sol-Gel Method

We have investigated on the synthesis of Ba_{1 – x}Sr_xTiO₃ (BST, x = 0.0–1.0) solid solution at low temperature by a sol-gel method using precursor solutions of Ba(OC₂H₅)₂, Sr(OC₂H₅)₂, and Ti(OCH(CH₃)₂)₄ dissolved in 2-methoxyethanol. Crystalline BST solid solution monolithic gels were obtained as dried at 90°C. Crystalline fraction of BST gels increased with increasing concentration of the precursor solution and increasing amount of the hydrolysis water used. Ba_0.4Sr_0.6TiO₃ (x = 0.6) gels from a precursor solution of 0.5 mol/l with hydrolysis water of H₂O/Ti = 50 crystallized during aging at 30°C.     

Pyrolysis of eicosane in supercritical water

Pyrolysis of eicosane and redox reactions of the pyrolysis products in supercritical water (SCW) were studied in a batch reactor at 30 MPa, in the temperature range from 450 to 750 °C and with reaction times ranging from 75 to 600 s. The rate constants for eicosane pyrolysis (k" = 10^16.5±0.5exp[–(32000±2000)/T] s^–1) and for the formation of H₂ (k = 10^25±0.8exp[–(64000±4000)/T] s^–1) were determined. The time and temperature dependences of the heat of reaction were elucidated. Water accelerates pyrolysis and participates in the subsequent transformations of the pyrolysis products. The yield of H₂ sharply increases for T > 700 °C.     

Spectra and structure of organophosphorus compounds: XLIX. Microwave,infrared, and Raman spectra,electric dipole moment,molecular structure,and ab initio calculations of dimethylphosphonothioic fluoride

The microwave spectra of (CH₃)₂PSF, (CH₃)(CD₃)PSF, (CD₃)₂PSF, and (CH₃)₂P³⁴SF have been investigated from 20.0 to 40.0 GHz. Botha-type R branch andc-type Q branch transitions have been measured in the ground states of each isotopic species. From a least-square adjustment to fit 12 rotational constants, the following structural parameters were obtained:r(P–F)=1.582 ± 0.003 Å;r(P=S)=1.902 ± 0.001 Å;r(P-C)=1.800 ± 0.001 Å;r(C-H)=1.088 ± 0.002 Å; HCP=109.28 ± 0.12°; SPF=114.50 ± 0.13°; and SPC=116.33 ± 0.06°. From Stark effect measurements, the dipole moment components have been determined to be ¦ _a ¦ =3.556 ± 0.005; ¦ _c ¦=2.026 ± 0.009; and ¦ _t ¦=4.093 ± 0.009 (D). The Raman spectra (3200 to 100 cm^–1) of each isotopic species have been measured for the solid, and liquid and qualitative depolarization values obtained. Additionally, the mid-infrared spectra (3200 to 500 cm^–1) of the solids have been recorded. Proposed assignments of the normal modes have been made on the basis of Raman depolarization values and group frequencies which are supported by normal coordinate analysis utilizing an ab initio force field. Optimized structural parameters have been obtained with both the 3-21G^* and 6-31G^* basis sets. These results are compared to the corresponding quantities for several similar molecules.For part XLVIII, seeJ. Raman Spectrosc.1922,23, 107.     

Crystal structures and thermal properties of Ba(1,2,4-t-Bu3C5H2)2 and Sr(1,2,4-t-Bu3C5H2)2: Precursors for atomic layer deposition

Sterically hindered Lewis base free bis(1,2,4-tri-tert-butylcyclopentadienyl)strontium (1) and bis(1,2,4-tri-tert-butylcyclopentadienyl)barium (2) were synthesized using the common metathesis route and characterized with NMR, MS, TGA/SDTA and XRD. Compound 1 crystallized as a monomer with typical bent structure. Asymmetric unit contains two independent slightly different Sr(t-Bu₃C₅H₂)₂ molecules with Cp(centroid)-Sr-Cp(centroid) angles of 165.1° and 169.4°. Depending on the way of crystallization two polymorphs (2a and 2b) were observed for Ba(t-Bu₃C₅H₂)₂. On sublimation Ba(t-Bu₃C₅H₂)₂ crystallizes as chains in which one methyl group of each Ba(t-Bu₃C₅H₂)₂ unit interacts with neighboring Ba(t-Bu₃C₅H₂)₂ unit’s barium atom. Slow crystallization of waxy evaporation residue of toluene solution results in monoclinic crystals (2b) whose asymmetric unit contains four slightly different individual Ba(t-Bu₃C₅H₂)₂ molecules with Cp(centroid)-Ba-Cp(centroid) angles of 161.3-164.9°. Both compounds prepared are volatile, thermally stable and reactive and thus suitable precursors for atomic layer deposition of thin films.     

Sol-Gel Derived Ferroelectric Thin Films: Avenues for Control of Microstructural and Electric Properties

The paper presents short review of the works performed during the last few years in the field of the alkoxy-derived ferroelectric films. PZT films were prepared using titanium and zirconium alkoxides and Pb(CH₃COO)₂· 2H₂O as precursors. Different way of lead acetate dehydration and the impact of lead excess in the precursor solutions on the properties of the PZT films are discussed. Trimetallic alkoxide systems Bi(OR)₃-Ta(OR)₅-ROH (R = Me, Et or ⁱ Pr) were studied as precursors for preparation of SrBi₂Ta₂O₉ films. Films prepared from these solutions and annealed at the temperature between 700 and 750°C demonstrated the remanent polarization P_r* – P^{^} _r = 7–9 C/cm². Ba_1-xSr_xTiO₃ films we applied from modified alkoxide solutions. Decomposition of the organic phase in the course of thermal treatment of the films is studied by IR-spectroscopy. The dependence of the dielectric permittivity of the films via the annealing temperature is reported. Preparation of LiNbO₃, SrZr_0.2Ti_0.8O₃, Zr_0.8Sn_0.2TiO₄ is briefly discussed.     

Distribution of Strontium in the System Water — Ca(NO3)2 — Nitrobenzene — Strontium Dicarbollylcobaltate — 18-crown-6

From several strontium distribution experiments with ⁸⁵Sr tracer, the extraction constant corresponding to the equilibrium Ca²⁺(aq)+SrL²⁺(nb) CaL²⁺(nb)+Sr²⁺ (aq) in the two-phase water-nitrobenzene system (L = 18-crown-6; aq = aqueous phase, nb = nitrobenzene phase) was tentatively evaluated as log K _ex (Ca²⁺,SrL²⁺) = –1.9±0.1. Furthermore, the stability constant of the calcium — 18-crown-6 complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log _nb(Cal²⁺) = 10.1±0.1.     

Thermochemistry of Amines: Experimental Standard Molar Enthalpies of Formation of N-Alkylated Piperidines

The standard molar enthalpies of formation _f H _m ^° (l) at the temperature T = 298.15 K were determined using combustion calorimetry for N-methylpiperidine (A), N-ethylpiperidine (B), N-propylpiperidine (C), N-butylpiperidine (D), N-cyclopentylpiperidine (E), N-cyclohexylpiperidine (F), and N-phenylpiperidine (G). The standard molar enthalpies of vaporization _l ^g H ^{m °} of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. From these data the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) were derived for: A –(61.39 ± 0.88); B –(88.1 ± 1.3); C –(105.81 ± 0.66); D –(126.2 ± 1.3); E ( –88.21 ± 0.75); F –(135.21 ± 0.94); G (70.3 ± 1.4) kJ · mol^–1. They are used to determine the strain enthalpies of the cyclic amines A–G. The N-alkylated piperidine rings have been found to be about strainless.     

Synthesis, spectroscopy and structures of palladium(II) and platinum(II) complexes containing mercapto-o-carborane

The reactions of [M₂Cl₂(μ-Cl)₂(PMe₂Ph)₂] with mercapto-o-carboranes in the presence of pyridine afforded mono-nuclear complexes of composition, [MCl(SCb°R)(py)(PMe₂Ph)] (M = Pd or Pt; Cb° = o-C₂B₁₀H₁₀; R = H or Ph). The treatment of [PdCl₂(PEt₃)₂] with PhCb°SH yielded trans-[Pd(SCb°Ph)₂(PEt₃)₂] (4) which when left in solution in the presence of pyridine gave another substitution product, [Pd(SCb°Ph)₂(py)(PEt₃)] (5). The structures of [PdCl(SCb°Ph)(py)(PMe₂Ph)] (1), [Pd(SCb°Ph)₂(PEt₃)₂] (4) and [Pd(SCb^oPh)₂(py)(PEt₃)] (5) were established unambiguously by X-ray crystallography. The palladium atom in these complexes adopts a distorted square-planar configuration with neutral donor atoms occupying the trans positions. Thermolysis of [PdCl(SCb°)(py)(PMe₂Ph)] (2) in TOPO (trioctylphosphine oxide) at 200 °C gave nanocrystals of TOPO capped Pd₄S which were characterized by XRD pattern and SEM.     

Phase formation in the systems Ag2MoO4-MO-MoO3 (M=Ca, Sr, Ba, Pb, Cd, Ni, Co, Mn) and crystal structures of Ag2M2(MoO4)3 (M=Co, Mn)

Phase equilibria in the systems Ag₂MoO₄-MMoO₄ (M=Ca, Sr, Ba, Pb, Ni, Co, Mn) and subsolidus phase relations in the systems Ag₂MoO₄-MO-MoO₃ (M=Ca, Pb, Cd, Mn, Co, Ni) were investigated using XRD and thermal analysis. The systems Ag₂MoO₄-MMoO₄ (M=Ca, Sr, Ba, Pb, Ni) belong to the simple eutectic type whereas in the systems Ag₂MoO₄-MMoO₄ (M=Co, Mn) incongruently melting Ag₂M₂(MoO₄)₃ (M=Co, Mn) were formed. In the ternary oxide systems studied no other compounds were found. Low-temperature LT-Ag₂Mn₂(MoO₄)₃ reversibly converts into the high-temperature form of a similar structure at 450-500°C. The single crystals of Ag₂Co₂(MoO₄)₃ and LT-Ag₂Mn₂(MoO₄)₃ were grown and their structures determined (space group , Z=2; lattice parameters are a=6.989(1) Å, b=8.738(2) Å, c=10.295(2) Å, α=107.67(2)°, β=105.28(2)°, γ=103.87(2)° and a=7.093(1) Å, b=8.878(2) Å, c=10.415(2) Å, α=106.86(2)°, β=105.84(2)°, γ=103.77(2)°, respectively) and refined to R(F)=0.0313 and 0.0368, respectively. The both compounds are isotypical to Ag₂Zn₂(MoO₄)₃ and contain mixed frameworks of MoO₄ tetrahedra and pairs of M²⁺O₆ octahedra sharing common edges. The Ag⁺ ions are disordered and located in the voids forming infinite channels running along the a direction. The peculiarities of the silver disorder in the structures of Ag₂M₂(MoO₄)₃ (M=Zn, Mg, Co, Mn) are discussed as well as their relations with analogous sodium-containing compounds of the structural family of Na₂Mg₅(MoO₄)₆. The phase transitions in Ag₂M₂(MoO₄)₃ (M=Mg, Mn) of distortive or order-disorder type are suggested to have superionic character.