Influence of YSZ buffer layer on the electric properties of compositionally graded (Ba,Sr)TiO<Subscript>3</Subscript> thin film

Compositionally graded Ba_1−x Sr _x TiO₃ (BST) (0 ≤ x ≤ 0.4) thin films were fabricated on Pt/Ti/SiO₂/Si and YSZ/Pt/Ti/SiO₂/Si substrates by a modified sol–gel technique. The YSZ buffer layer was prepared by RF magnetron sputtering. The microstructure of the graded BST films was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results showed that all the films have uniform and crack-free surface with a perovskite structure. The graded BST film with an YSZ buffer layer has larger dielectric constant and lower dielectric loss. The leakage current density of the graded BST film with an YSZ buffer layer lowers two orders than the film without buffer layer. The improved electric properties of the graded films with an YSZ buffer layer was attributed to the YSZ buffer layer act as an excellent seeding layer to enhance the graded BST film growth.     

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.     

(Ba<Subscript>0.93</Subscript>Nd<Subscript>0.07</Subscript>)TiO<Subscript>3</Subscript> thin films prepared by sol–gel method as a potential dielectric resonator antenna application

In this paper, we report the application of Neodymium (Nd) doped barium titanate thin films (Ba_1-xNd_x) TiO₃ with x = 0 and 0.07 as dielectric resonator antenna. The films were prepared using the sol–gel method and dip-coating technique. Barium acetate, titanium (IV) isopropoxide and neodymium (III) acetate hydrate were used as precursors while glacial acetic acid and acetylacetone were used as solvents. Si wafers were used as a substrate with dipping times varying from 10, 30, and 50 s. The 0.07 films were >800 nm thick and crystallized after being annealed at 800°C for 30 min. The films were tested as dielectric resonator antenna. It was found that, on the actual antenna circuit, the resonant frequency decreased as the (Ba_0.93Nd_0.07) TiO₃ films thickness increased (from 0.8379, to 5.4525 μm). All samples resonate in the range of 8.68–8.83 GHz with quasi omni-directional radiation patterns.     

Synthesis of electrospun BaSrTiO<Subscript>3</Subscript>/PVP nanofibers

Ba_1−x Sr _x TiO₃(x = 0–0.5, BST) nanofibers with diameters of 150–210 nm were prepared by using electrospun BST/polyvinylpyrrolidone (PVP) composite fibers by calcination for 2 h at temperatures in the range of 650–800 °C in air. The morphology and crystal structure of calcined BST/PVP nanofibers were characterized as functions of calcination temperature and Sr content with an aid of XRD, FT-IR, and TEM. Although several unknown XRD peaks were detected when the fibers were calcined at temperatures less than 750 °C, they disappeared with increasing the temperature (above 750 °C) due to its thermal decomposition and complete reaction in the formation of BST. In addition, the FT-IR studies of BST/PVP fibers revealed that the intensities of the O–H stretching vibration bands (at 3430 and 1425 cm⁻¹) became weaker with increasing the calcination temperature and a broad band at 540 cm⁻¹, Ti–O vibration, appeared sharper and narrower after calcination above 750 °C due to the formation of metal oxide bonds. However, no effect of Sr content on the crystal structure of the composites was detected.     

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.     

Preparation of Ba(Ti,Sn)O<Subscript>3</Subscript> thin films by PVP-assisted sol–gel method and their dielectric properties

Ba(Ti_1−x Sn _x )O₃ (x = 0.10 or 0.15) thin films were deposited on Si(100) and Pt(111)/TiO _x /SiO₂/Si(100) substrates via sol–gel spin-coating. Crack-free thin films could be obtained by single-step deposition, where the thickness was about 0.46 and 0.29 μm at 1000 and 2000 rpm, respectively. Circular delaminated parts 100 μm in diameter, however, tended to appear in thicker films deposited at 1000 rpm. On both kinds of substrates, the films were crystallized between 500 and 600 °C, where the perovskite phase emerged as the primary phase, and the formation of single-phase perovskite was basically achieved between 700–800 °C. The films deposited on Pt(111)/TiO _x /SiO₂/Si(100) substrates, however, tended to have small SnO₂ and BaCO₃ diffraction peaks, which decreased with increasing spinning rate. The dielectric properties were evaluated on the films deposited on Pt(111)/TiO _x /SiO₂/Si(100) substrates at 2000 rpm. The films prepared by single-step depositions had dielectric constants of 350 and 230, and dielectric loss of 0.30 and 0.10 at x = 0.1 and 0.15, respectively. The films prepared by two time deposition had dielectric constants of 450 and 250, and dielectric loss of 0.21 and 0.19 at x = 0.10 and 0.15, respectively.     

Domain reorientation dynamics of sol–gel derived strontium doped PLZT (8/65/35)

Polycrystalline samples of PLSZT with the composition Pb_0.92−x La_0.08Sr _x (Zr_0.65Ti_0.35)O₃ (where x = 0, 0.02, 0.04, 0.06, 0.08, and 0.10) have been synthesized by sol–gel technique. DTA analysis confirms that all the organic constituents get decomposed and final PLZT is formed at 545 °C. The XRD analysis suggests the formation of single rhombohedral perovskite phase with decreasing unit cell parameter. Crystallite size calculated, using Scherrer’s equation, was found to decrease with Sr doping due to smaller ionic radii of Sr than Pb. Compact uniform grain distribution was observed from SEM micrographs. The ferroelectric to paraelectric phase transition temperature, maximum dielectric constant and remanent polarization (P _r) were found to decrease with Sr doping along with increasing diffuse nature of phase transformation. Detailed domain reorientation dynamics study suggests that Sr doping increases the percentage backswitching and decreases the normalized coercivity by decreasing the viscous nature of composition.     

Etude des systemes CaHPO4−MHPO4−H2O (M=Sr,Ba) A 50°C

The systems CaHPO₄−MHPO₄−H₂O (M=Sr, Ba) were studied at 50°C. ForM=Sr, the series of single phases, Ca_1−xSr_xHPO₄ for 0.95<X<0.75 and Ca_xSr_1−xHPO₄ for 0.4<X<1 have been prepared. These solid solution were caracterized by their infrared spectra and their crystallographic unit cell parameters. ForM=Ba a new phase Ca₂Ba(HPO₄)₃ has been determined. It was characterized by DRX, IR, ATD and chemical analyses.

---

Zusammenfassung Bei 50°C wurde das System CaHPO₄−MHPO₄−H₂O (mitM=Sr, Ba) untersucht. FürM=Sr wurden Serien von Einzelphasen erhalten: Ca_1−xSr_xHPO₄ für 0.95<X< 0.75 und Ca_xSr_1−xHPO₄ für 0.4<X<1. Diese Mischkristalle wurden anhand ihrer Infrarotspektren und ihrer kristallographischen Elementarzellenparameter charakterisiert. FürM=Ba wurde die neue Phase Ca₂Ba(HPO₄)₃ ermittelt. Sie wurde mittels DRX, IR, ATD und chemischer Analyse charakterisiert.

     

Pyridine based cerium(IV) phosphate hybrid fibrous ion exchanger

Both temperatures, T _C, (T _C —Curie temperature) and heat of the phase transition: ferroelectric-paraelectric, ΔH, in the Ba_xSr_1−xTiO₃ materials have been studied by means of the microcalorimetric method. The determined parameters were verified by either temperature dependence of the dielectric permittivity (Curie-Weiss law) or thermodynamic method. The effect of strontium content on T _C has been discussed. It was found that microcalorimetry is useful tool studying phase transition phenomena in ferroelectric perovskites.     

Study of dielectric characteristics of graded Ba<Subscript>1−x</Subscript>Ca<Subscript>x</Subscript>Zr<Subscript>0.05</Subscript>Ti<Subscript>0.95</Subscript>O<Subscript>3</Subscript> thin films grown by a sol-gel process

The compositionally graded Ba_1−xCa_xZr_0.05Ti_0.95O₃ (x = 0, 0.05, 0.10) (BCZT) thin films with compositional gradient from BaZr_0.05Ti_0.95O₃ to Ba_0.90Ca_0.10Zr_0.05Ti_0.95O₃ were deposited on Pt/Ti/SiO₂/Si substrates by sol-gel processing. The crystal structure of the thin films was determined by X-ray diffraction. Field emission scanning electron microscopy (FESEM) was used to examine crystallite size and morphology of compositionally graded thin films. The dielectric properties of compositionally graded thin films were characterized by measuring the dielectric constant and dielectric loss as a function of temperature, applied electric field and frequency. As a result, compositionally graded thin films with weak temperature dependence were realized. Dielectric constant peaks, common to a ferroelectric transition, were not observed in the temperature range from 298 to 413 K. The compositionally graded BCZT thin films with weak temperature dependence of tunability could be attractive materials for frequency and phase agile tunable microwave components such as tunable filters, tunable oscillators, and phase shifters for application in phased array antennas.     

State of atoms and interatomic interactions in complex perovskite-like oxides: XXX. Influence of the nature of diamagnetic substituents on the dynamics of clustering in lanthanum gallate doped with strontium,chromium, and magnesium

The fractions of clusters and single chromium atoms were calculated by the diluted solution and Heisenberg-Dirac-van-Vleck models for a series of solid solutions containing chromium, strontium, and magnesium in the ratio 5:1:1, respectively. A principal genetic relationship was revealed between La_1−0.2x Sr_0.2x ·Cr _x Ga_1−x O_3−δ, La_1−0.5x Sr_0.5x Cr _x Ga_1−x O_3−δ, and La_1−0.2x Sr_0.2x Cr _x Ga_1−1.2x Mg_0.2x O_3−δ systems. Deviations from Curie-Weiss law are observed for the systems with the ratio [Cr]:[Sr]:[Mg]=5:1:1, which point to a noncompensated magnetic moment.     

Ionic conductivity of multicomponent fluorite-structured fluorides

Influence of mixing of homovalent cations on the fast anionic conductivity, static permittivity, and thermal diffusivity is investigated in multicomponent fluorite-structured concentrated solid solutions of alkali earth and rare earth fluorides. Influence of mixing of alkali earth cations on electrical properties of fluoride superionics is studied in Ba_{0.7 − x} Sr _x La_0.3F_2.3 single crystals and Ca_{0.85 − x} Sr _x Nd_0.15F_2.15 transparent polycrystals. Influence of mixing of rare earth cations on electrical properties of fluoride superionics is studied in Ba_0.75La_{0.25 − x} Nd _x F_2.25 and Ba_0.35Sr_0.35(R ₁, ..., R _i )_0.3F_2.3 (i = 1–6; R _i stands for rare earth elements) single crystals. It is shown that the ionic conductivity decreases with increasing difference between mean ionic radii of rare earth and alkali earth cations. Up to 350°C, the fastest ionic conductivity is found in Ba_0.35Sr_0.35La_0.3F_2.3 single crystals.     

Hydrolysis behavior of a precursor for bridged polysilsesquioxane 1,4-bis(triethoxysilyl)benzene: a <Superscript>29</Superscript>Si NMR study

The hydrolysis behavior of 1,4-bis(triethoxysilyl)benzene (BTB), a precursor of bridged polysilsesquioxane, was investigated with high-resolution ²⁹Si nuclear magnetic resonance (²⁹Si NMR) spectroscopy at ambient temperature in a system with BTB:ethanol:water:HCl = 1:10:x:0.8 × 10⁻⁴ (x = 3, 6 or 9). Signals due to hydrolyzed triethoxysilyl groups as well as unhydrolyzed triethoxysilyl groups [−Si(OEt)₃, −Si(OEt)₂(OH), −Si(OEt)(OH)₂ and −Si(OH)₃ (OEt = OCH₂CH₃)] formed four sub-regions based on the number of hydroxyl groups bound to a silicon atom. In addition, one silicon environment influenced the other silicon environment by an intra-molecular interaction between two silicon atoms, and each sub-region for monomeric species thus contained four signals. Based on the development of signal intensity, it is revealed that one of the two triethoxysilyl groups in BTB is hydrolyzed preferentially. Thus, when a triethoxysilyl group is hydrolyzed, the −Si(OH) _x (OEt)_3−x (x = 1, 2) groups formed undergo further hydrolysis, which is opposite to the tendency expected from the hydrolysis behavior of organotrialkoxysilanes under acidic conditions.     

Thermal expansion and heat capacity measurements on Ba10?xCsx(PO4)6Cl2?δ, (x?=?0, 0.5) chloroapatites synthesized by sonochemical process

Ba_10−x Cs _x (PO₄)₆Cl₂, (x = 0, 0.5) chloroapatite ceramics were prepared by sonochemical method of synthesis. The measured room temperature lattice parameters of Ba₁₀ (PO₄)₆Cl₂ and Ba_9.5Cs_0.5 (PO₄)₆Cl_2−δ are practically the same; that is, a = 10.26 (8), c = 7.65 (7) and a = 10.27 (7), c = 7.65 (5), respectively. Heat capacity measurements were carried out on these materials by differential scanning calorimetry (DSC) in the temperature range 298–800 K. The heat capacity values of Ba_9.5Cs_0.5(PO₄)₆Cl_2−δ are found to be slightly higher at all temperatures than those of Ba₁₀(PO₄)₆Cl₂. From the heat capacity data, other thermodynamic functions such as enthalpy and entropy increments were computed. The heat capacity values of Ba₁₀(PO₄)₆Cl₂ and Ba_9.5Cs_0.5(PO₄)₆Cl_2−δ at 298 K are 0.3912 and 0.4310 J K⁻¹ g⁻¹, respectively. Thermal expansion property of the doped and undoped barium chloroapatites was measured by using a home built dilatometer which uses LVDT as displacement sensor. The bulk thermal expansion of Ba₁₀(PO₄)Cl₂ and Ba_9.5Cs_0.5(PO₄)Cl_2−δ is observed to be about 0.9% in the temperature range of 298–973 K.     

Improved electric properties in BiFeO3 films by the doping of Ti

We prepared BiFe_1−x Ti _x O_3+δ (BFTO) films by sol gel process and various oriented films were deposited on LaNiO₃ coated SiO₂/Si substrates with different x. The effects of Ti substitution on dielectric, ferroelectric, magnetic and leakage conduction properties in BFTO system have been studied. Enhanced ferroelectricity was observed at room temperature due to the substitution of Ti. The largest double remnant polarization of 3.8 μC/cm² was acquired in the film with x = 0.10. Further more, it was observed that the dielectric constants were also enhanced by the substitution of Ti. The film with x = 0.10 has the largest dielectric constant below 100 kHz and Debye-like relaxation were observed in the films with x = 0.05 and 0.10. The leakage conduction was reduced with the increasing of the content of Ti. More over, the magnetism was also altered by the substitution.     

Physicochemical properties of non-stoichiometric oxides

One of the most important challenges with solid oxide fuel cells (SOFC) is to find cathode materials with high enough catalytic activity for the dissociation of the molecular oxygen. Oxide mixed conductors with the perovskite structure (ABO₃) and high Co content in the B site have been extensively studied to be used as cathode in SOFC. This is the second part of a review of high temperature properties of two mixed conductors systems. The first part was focused on the n = 2 Sr₃FeMO_6+δ (M = Fe, Co, Ni) Rudlesdden Popper phases, while in this paper we discuss the thermodynamic and transport properties of the perovskite solid solution Sr_1−x La _x Fe_0.2Co_0.8O_3−δ (0 ≤ x ≤ 0.4) in the temperature range 773 ≤ T ≤ 1173 K. In particular, the interest has been focused on the x = 0 sample, which exhibits large ionic conductivity values (σ_i ~1 S cm⁻¹), but suffers a structural transformation from cubic to orthorhombic symmetry because the ordering of the oxygen vacancies when the oxygen partial pressure decreases. Measurements of the oxygen chemical potential ( m_\textO2 \mu_{{{\text{O}}_{2} }} ) as function of oxygen content and temperature, coupled with high temperature X-ray diffraction data, permitted us to broaden the knowledge of the T–δ–p(O₂) phase diagram for the x = 0 sample. In addition, we have investigated the effects of the La incorporation on the stability range of the cubic phases of the Sr_1−x La _x Fe_0.2Co_0.8O_3−δ solid solution.     

PMMA-SiO<Subscript>2</Subscript> organic–inorganic hybrid films: determination of dielectric characteristics

Organic–inorganic hybrid thin films have been prepared by a modified sol–gel route using tetraethyl orthosilicate as the inorganic (silica) source, methyl methacrylate (MMA) as the organic source, and 3-trimetoxysilylpropyl methacrylate as the coupling agent. The films were prepared by spin coating on Si (100) p-type substrates and subsequently heat-treated at 90 °C. Fourier transform infrared results reveal a set of absorption bands associated with the formation of both PMMA and SiO₂ phases in the hybrid films. Capacitance–voltage (C–V) characterization was carried out on metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) structures, with the hybrid films as the insulator layer to evaluate the electrical properties. We present a detailed comparative analysis of the dielectric constant obtained from C–V characterization in the frequency range of 1 kHz–1 MHz. For the PMMA-SiO₂ hybrid material the dielectric constant values obtained were around 9.5 at 1 MHz which is superior to the values reported for thermally grown SiO₂ and pure PMMA materials. The interface state density for PMMA-SiO₂ on Si was approximately 10¹⁰ cm⁻², which is comparable to the standard SiO₂/Si structures. Due to the electrical behavior and low processing temperatures this hybrid dielectric is a very promising candidate for flexible electronic devices and its subsequent implementation does not require complex equipment.     

Structural and morphological characteristics of (Pb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)TiO<Subscript>3</Subscript> powders obtained by polymeric precursor method

Pb_1−x Sr _x )TiO₃ powders with different compositions (x = 0, 0.10, 0.50, 0.90 and 1) were synthesized by the polymeric precursor method and heat treated at 800 °C for 2 h under air atmosphere. The thermogravimetric and differential scanning calorimetry analyses were performed in the range from 25 to 800 °C in order to estimate the stages corresponding to the water evaporation, organic decomposition and crystallization of these materials. X-ray diffraction patterns and Rietveld analyses showed that the (Pb_1−x Sr _x )TiO₃ phases with strontium content up to x = 0.1 crystallize in a tetragonal structure. The micrographs obtained by scanning electron microscopy and transmission electron microscopy showed that the powders have agglomerated nature, presenting irregular morphologies and polydisperse particle size distribution. The energy dispersive X-ray spectrometry indicated the presence of pure (Pb_0.50Sr_0.50)TiO₃ phase.     

Structure and properties of films based on HfO<Subscript>2</Subscript>-Sc<Subscript>2</Subscript>O<Subscript>3</Subscript> double oxide

The results of the investigation of the chemical constitution and structure of (HfO₂) _x (Sc₂O₃)_1−x thin films are reported. The films are obtained by chemical vapor deposition (CVD) from hafnium 2,2,6,6-tetramethyl-3,5-heptandionate (Hf(thd)₄) and scandium 2,2,6,6-tetramethyl-3,5-heptandionate (Sc(thd)₃) coordination compounds. It is demonstrated by powder X-ray diffraction and infrared spectroscopy that depending on the scandium content in the films the structure is changed from monoclinic to cubic. Voltage-capacity dependences of test Al/(HfO₂) _x (Sc₂O₃)_1−x /Si structures are used to calculate the dielectric constant of the films. For the films with the cubic structure it is found that k = 21, while for the films with the monoclinic structure k = 9.     

Investigation of s, p, d-element Niobates and Their Solid Solution Formation Processes by Thermal Analysis

The binary and ternary systems M'O(M'CO₃)-Nb₂O₅ and M'O(M'CO₃)-MO-Nb₂O₅, where M'=Ca,Sr and Ba and M=Cu, Ni, Cd, Zn and Pb, were investigated by means of thermal analysis in the temperature range 20–1500°C. The boundaries of stability of the solid solutions Sr_2−xMe_xNb₂O₇,Sr_2−xM_xNb₂O₇, Sr_4−xM_xNb₂O₉ and Sr_6−xM_xNb₂O₁₁ were determined by means of X-ray diffraction, and IR and Raman spectroscopy. The possibility of prognostication of the phase fields of stable solid solutions by calculation from the diagrams of the ‘comparative electronegativity of atoms vs. tolerance factor’ was demonstrated. The kinetic parameters of the interactions in theSrCO₃+MO+Nb₂O₅ powder mixtures were established. This revised version was published online in August 2006 with corrections to the Cover Date.