Crystalline Barium Research Articles

As-deposited crystalline barium ferrite thin film media for longitudinal recording

Using facing target sputtering, crystalline barium ferrite (BaFe 12O 19, BaM) has been deposited onto a silicon nitride coated carbon substrate, producing high-quality, randomly oriented crystalline films in-situ at a substrate temperature of 640°C without post-deposition annealing. Using inductive read-write heads, longitudinal recording tests reveal that randomly oriented BaM thin films have a linear recording density ( D 50) greater than 100 kfci and a high signal to noise ratio (∼39 dB). The low noise performance of BaM thin film is consistent with its measured small and negative ΔM value, indicating no intergranular exchange interaction. It is argued that BaM is intrinsically a low-noise medium with exchange decoupled grains, regardless of how the grains are oriented and how dense the sputtered films are.

Thermally activated crystalline phase restoration in disordered barium ferrite powder prepared by ball milling

Depending on milling conditions (air or vacuum) for the same milling time, a different level of decomposition and structure disorder in BaFe12O19 ferrite powders can be obtained by ball milling. Air-milled material has a tendency to form a gas-saturated disordered structure (superoxide) and to transform into simple oxides (reduction process through oxygen-saturated disordered phase) as opposed to the vacuum-milled powder where a highly disordered phase occurs. Both powders have a different morphology (particle size and distribution). Annealing processes produce crystalline barium ferrite phase with interesting magnetic properties, but in the present paper only structural transformations are analysed. Scanning electron microscopy, X-ray diffraction and thermal analysis techniques were applied to study the effects of heat treatment (10 h at 773 or 1273 K) in disordered BaFe12O19 ferrite powders prepared by 1000 h ball milling in air and vacuum.

Reaction-mediated texturing of barium ferrite magnetic thin films on ZnO underlayer

Using facing target sputtering, crystalline magnetoplumbite-type barium ferrite (BaFe12O19 or BaM) thin films have been prepared in situ at a substrate temperature of 640 °C without postdeposition annealing. Using our facing target sputtering system, BaM thin films grow randomly if they are directly deposited onto Si or thermally oxidized Si substrates. However, deposited onto a sputtered ZnO layer (∼230 Å) on Si substrates, BaM thin films show excellent c-axis out-of-plane texture with a 0.2°c-axis dispersion angle, as indicated by x-ray diffraction (XRD). Cross-section transmission electron microscopy (XTEM) reveals that the textured films epitaxially grow on a transition layer, which is formed between BaM and ZnO. No direct epitaxial relation between BaM and ZnO was observed. This transition layer is identified by TEM and XRD as ZnFe2O4, which, from a structure point of view, reduces the lattice mismatch between BaM and ZnO, and also enhances the c-axis out-of-plane epitaxial growth. ZnFe2O4 is a reaction product of BaM and ZnO, as indicated by both TEM and XRD. After ex situ annealing the film in air at 800 °C, the ZnFe2O4 layer becomes thicker at the expense of BaM and ZnO. The lattice parameters of both BaM and ZnO decreased as annealing time increased.

Preparation of monolithic barium titanate xerogels by sol–gel processing and the dielectric properties of their sintered bodies

Monolithic xerogels of crystalline barium titanate, with dimensions of ∼3 mm thick and ∼6 mm in diameter, have been produced by sol–gel processing using metal alkoxides. An excess amount of water with the H2O/Ba ratio≳100 (for hydrolysis of the barium titanate precursor alkoxides) and aging time≳8 days were necessary to produce the monolithic crystalline xerogels without breaking during drying (at 90 °C). The barium titanate xerogels as-dried, with a porosity of about 70%, have been found to consist of crystalline grains in the range of 10–20 nm. Firing the xerogels at 1000 °C in air yielded porous barium titanate ceramics with an average grain size around 50 nm and a decreased porosity around 60%. The dielectric constant (εr)–temperature (T) characteristics of these ceramics have been found to be rather flat below 120 °C with a broad peak around this temperature, and those above 120 °C showed a specific behavior of ferroelectric materials described by a Curie–Weiss equation, εr=C/(T–T0), with C≊2×104 K and T0≊230 K (−43 °C); although these values are quite different from those of ferroelectric barium titanate.

Microstructural investigations of barium ferrite longitudinal thin-film media

Crystalline barium ferrite films with in-plane magnetic anisotropy have been obtained by postdeposition annealing of amorphous sputtered films. The magnetic properties, the crystallographic texture, and the microstructure are very sensitive to the sputtering and postdeposition annealing conditions. It was found that both Hc and the grain size decrease with the addition of Co and Ti ions. However, an excessive amount of dopants leads to a loss in the in-plane anisotropy. Barium ferrite films produced by this technique contain physical voids or channels separating the grains which help to decrease the exchange coupling between grains.

Synthesis of bismuth/strontium/calcium/copper and yttrium/barium/copper oxide systems from malonate precursors

Malonate salts of the above metals dissolved in a glycerol/malonic acid polyester have been found to form amorphous oxide systems at relatively low temperatures. Mixtures of the appropriate stoichiometry rapidly form the corresponding 2212 BSCCO and tetragonal YBCO oxide systems on heating to temperatures in the range 750–850 °C. In the case of YBCO, the formation of crystalline barium carbonate can be largely suppressed by an appropriate thermal programme, but whereas the tetragonal YBCO6.5 phase can be readily obtained as the sole crystalline phase, oxygen diffusion into this phase is remarkably difficult. This appears to be due to the presence of amorphous intergranular material.

Pathways for the low temperature synthesis of nano-sized crystalline barium zirconate

Abstract The low temperature (below 100 °C) sol-precipitation synthesis of nano-sized and crystalline barium zirconate (BaZrO3) powders is discussed. Structural evolution of crystalline BaZrO3 phase was studied under sol-precipitation and hydrothermal conditions. Chemical analysis showed that the zirconium precursor precipitated during the early stages of the reaction ( t min ) led to nano-sized (10–100 nm) hydrous oxide primary particles. The alkaline earth cation, occluded in the entrained liquid, subsequently intercalated into the primary particles to transform originally amorphous transition metal-rich precipitates into crystalline BaZrO3 at temperatures as low as 90 °C. The precipitate crystal phase development exhibited a significant on time ( t=5–240 min ) and temperature (90–205 °C). Increasing time or temperature enhanced the formation of the perovskite phase. BaZrO3 synthesis was also characterized by another salient feature in that primary particles grew into fairly uniform (1–3 μm) pseudospherical secondary particles by what appeared to be a particle aggregation mechanism. This is one of the few systems that exhibit two simultaneous processes: (1) crystallization of primary particles with a chemical change and (2) formation of uniform, spherical secondary particles via particle aggregation.

Longitudinal recording performance of sputtered barium ferrite media on a carbon rigid disk substrate

We report the first measurement of the longitudinal magnetic recording properties of as-deposited crystalline thin film barium ferrite media. Using facing target sputtering, randomly oriented crystalline barium ferrite (BaFe/sub 12/O/sub 19/, BaM) has been deposited onto an Ultra Densified Amorphous Carbon substrate, producing high quality films in-situ at a substrate temperature of 660/spl deg/C without any post-deposition annealing. In order to prevent diffusion of carbon into the BaM film, an underlayer of silicon nitride was first reactively sputtered. The BaM sputtering was carried out using targets made from substituted BaM powder which had a powder H/sub c/=1860 Oe (from Toda Kogyo) in a 10% O/sub 2//Ar gas mixture at 3 mTorr. The sputtered films had an in-plane H/sub c/=2100 Oe. The performance of the disk was compared to a commercial disk with cobalt alloy media with H/sub c/=1760 Oe. At a flying height of 75 nm the isolated pulse width, PW/sub 50/, was 0.67 /spl mu/m vs. 0.88 /spl mu/m for the commercial media using a ReadRite M84 thin film head with a gap of 0.3 /spl mu/m. Near its measured D/sub 50/ of 66 kfci the BaM media had a broad band signal/noise ratio (SNR) of 20 dB vs. 13 dB for the commercial media. >

Interface Reaction Enhanced Epitaxial Growth of Barium Ferrite Magnetic Thin Films

AbstractUsing facing target sputtering, crystalline magnetoplumbite-type barium ferrite (BaFe12O19 or BaM) thin films have been prepared in-situ at a substrate temperature of 640°C without postdeposition annealing. BaM thin films grow randomly if they are directly deposited onto Si or thermally oxidized Si substrates. However, deposited onto a sputtered ZnO layer (∼230Å) on Si substrates, BaM thin films show excellent c-axis out-of-plane texture with a 0.2° c-axis dispersion angle, as indicated by X-ray diffraction (XRD) study. Cross section transmission electron microscopy (TEM) reveals that the textured films epitaxially grow on a transition layer, which is formed between BaM and ZnO. No direct epitaxial relation between BaM and ZnO was observed. This transition layer is identified by TEM and XRD as ZnFe2O4, which, from a structure point of view, reduces the lattice mismatch between BaM and ZnO, and also enhances the c-axis out-of-plane epitaxial growth.

Characterization of Sputtered Barium Ferrite Thin Films on Silicon Nitride Coated Carbon Substrates

AbstractUsing facing target sputtering, randomly oriented crystalline barium ferrite(BaFe12O19, BaM) has been deposited onto a Ultra Densified Amorphous Carbon® (UDAC) substrate, producing high quality films in-situ at a substrate temperature of 6400°C without any post-deposition annealing. Cross section transmission electron microscopy (TEM) reveals that the films have columnar structure. A ˜100Å thick interdiffusion layer between BaM and silicon nitride underlayer was observed. Films grown at low oxygen partial pressure have lower saturation magnetization (Ms), that may be caused by the formation of some amorphous phase at the grain boundaries as noticed by plan-view TEM. The existence of the Fe2O3 phase in the BaM was also revealed by electron diffraction.

Study of the boron-oxygen units in crystalline and molten barium metaborate by high temperature Raman spectroscopy

The vibrational spectra of the boron-oxygen structural elements in single crystal β-BaB 2O 4 and BaB 2O 4 melts were studied by high temperature Raman spectral analysis. The experimental Raman peaks were assigned to the calculated normal vibrational modes of the free [B 3O 6] molecular unit. The observed vibrational mode splittings were found to be consistent with C 6 3 v symmetry for β-BaB 2O 4. Experimental vibrational spectra were compared with those of LiBO 2 and CsBO 2 in order to determine the temperature-dependent populations of chain, ring, and tetrahedral structural elements in the respective melts, and these in turn were shown to correlate with the degree of melt supercooling required for spontaneous crystallization to occur.

An investigation of particle size effects in ultrafine barium ferrite

Ultrafine particles of barium ferrite in the size range 5–100 nm have been synthesized by thermal decomposition of a citrate precursor. The precursor decomposed at 425°C is amorphous, but crystalline barium ferrite starts forming at temperatures of 550°C and above. Barium ferrite which shows a monophase X-ray diffraction pattern and well-resolved Mössbauer spectra is obtained at 700°C. The Mössbauer spectra at both liquid helium and room temperature of samples annealed at 700, 750 and 800°C (with average particle sizes in electron micrographs of 60, 80 and 100 nm, respectively) could be satisfactorily resolved into five components corresponding to the five sublattice sites in barium ferrite. The Mössbauer parameters: magnetic hyperfine field, quadrupole splitting and isomer shift, all show particle size dependence. The magnetic hyperfine field and quadrupole splitting are smaller for smaller particles (compared to bulk barium ferrite) and they increase with increasing particle size and annealing temperature for all the five sublattice sites. Isomer shifts also differ from bulk values but the variation with particle size is also dependent on the sublattice sites.

High‐Performance Multilayer Capacitor Dielectrics from Chemically Prepared Powders

Advantages of chemically prepared powders for electronic ceramics have been demonstrated for a number of multilayer capacitor (MLC) dielectrics. A cost‐efficient precipitation process was developed to produce undoped or doped crystalline barium titanate powder with a narrow particle size distribution close to 0.5 μm. More complex compositions, e.g., barium‐neodymium titanate, were amorphous as precipitated but could be crystallized by calcination below 1000°C. Additional compositional modifications, to adjust electrical properties or to lower sintering temperature, were accomplished by doping the surface of the powder particles using a solution coating process. Exceptional fired densities and electrical performance were obtained.

Pressure-induced crystalline-to-noncrystalline transformations of barium fluorozirconates: A probe of the medium range order of noncrystalline solids

The reversible pressure-induced transformation of crystalline barium fluorozirconates to noncrystalline solids is reported. The transformation is observed by in situ high pressure Raman spectroscopy. Since the reported crystal-to-noncrystalline transformations occur reversibly, the medium range order (MRO) of the noncrystalline solid formed can be determined; there are very few experimental methods for determining the MRO of amorphous materials. Specifically, it is reported that crystalline β-BaZr2F10 becomes noncrystalline at 35–45 kb, α-BaZrF6 at 65–75 kb, and β-BaZrF6 at 100–120 kb. The medium range order for the noncrystalline phases formed at high pressures is as follows: those formed from β-BaZrF6 crystals consist of kinked chains of zirconium fluoride; noncrystalline materials formed from crystals of α-BaZrF6 contain chains which are connected in many directions forming a ‘‘net’’ of zirconium fluoride polyhedra; and crystals of β-BaZr2F10 form a solid composed of distorted layers of zirconium fluoride polyhedra. More succinctly, the high pressure noncrystalline phase of β-BaZrF6 is one dimensional, of α-BaZrF6 is somewhat three dimensional, and the solid formed from β-BaZr2F10 is fully two dimensional. This is the first report of a crystalline-to-noncrystalline transformation for a material which can be formed at ambient pressure as both a crystalline solid and as a melt-quenched glass. The relationship between the pressure-induced noncrystalline phases and their ambient pressure melt-quenched analogues is discussed.

Crystalline BaTiO3 Thin Film Prepared from Ti Metal by Hydrothermal-Electrochemical Method

ABSTRACTThin film of crystalline barium titanate, BaTiO3, has been prepared from Ti metal at 100–200°C by a new technique called “hydrothermal-electrochemical method” which could be categorized into a variety of the extended hydrothermal method. The reaction was carried out in an electrolytic cell containing 0.1–0.5N Ba(OH)2 aqueous solutions at temperatures of 100–200°C and under saturated vapor pressures. Titanium metal substrate or Ti-deposited glass substrate was used for the anode and a Pt plate for the cathode. Between the electrodes, a constant current density up to 100 mA/cm2 was applied galvanostatically for 10–80 min. Surface of the BaTiO3 film was lustrous and free from any visible defects. Thickness of the BaTiO3 films ranged from 70nm to 300nm. The adhesion between the film and substrate was so strong that no exfoliation was observed. Similar BaTiO3 thin films with thickness less than 70 nm were also formed even in simple hydrothermal conditions without applying any electric current.

Synthesis and characterization of gel-derived barium hexa-aluminate

Transparent barium hexa-aluminate gel was synthesized by chemical polymerization reactions involving commercial aluminium di(isopropoxide) acetoacetic ester and barium acetate. The gel was evaluated in terms of weight loss and thermal and crystallization characteristics by thermogravimetric analysis, differential thermal analysis, transmission electron microscope and X-ray diffraction. The as-prepared gel was amorphous to electron diffraction. X-ray diffraction results showed that fully crystalline barium hexa-aluminate can be produced at ≤1200°C which is 150°C less than the minimum synthesis temperature reported in the literature. The crystallization kinetics of the gel are discussed on the basis of the X-ray diffraction data. Furthermore, preliminary studies were conducted to examine the sintering behaviour of isostatically pressed pellets fabricated from 800°C heat-treated and milled gel powder. The sintered pellets were characterized in terms of density, microstructure, and linear thermal expansion. Sinterability of the material at 1550°C was unsatisfactory. The sintered density of the pellets was less than 60%. Microstructural examinations showed that sintered pellets were highly porous and consisted of a mixture of round, hexagonal plate-like and needle-like particles, the relative proportion of each type being dependent on the heat-treatment schedule. The linear expansion coefficient measured on a 1550°C sintered specimen was 7.3×10−6 in the 15 to 1000°C range.

Scintillator slurries of barium fluoride sand and index matched liquids

The authors investigated some of the scintillation properties of small quantities of crushed and ground crystalline barium fluoride powders or sands, wetted with a variety of fluid solutions closely matched in refractive index to the barium fluoride, forming a clear scintillator slurry with a density of about 3.8 g/cm/sup 3/ and a radiation length estimated to be about 2.8 cm. Some successful mixtures used novel liquid scintillators as the fluid base, providing a totally active scintillator detector matrix with a light output on a small sample about 30% of that produced by NaI. It is concluded that these heavy fluid or gel-like materials have the potential of creating relatively dense, short-radiation-length, fast, radiation-hard scintillators for large-scale calorimetric radiation detectors, with much lower cost than single-crystal detectors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Linear electro-optic effect in barium metaborate

We report the first measurement of the linear electro-optic coefficients of crystalline barium metaborate. The largest electro-optic coefficient r22 was found to be 2.5 pm/V, about four times smaller than the r63 of potassium dihydrogen phosphate (KDP). The dispersion of the electro-optic coefficient was also measured and found to be in excellent agreement with predicted values using the anharmonic oscillator model. Implications of the result on the point group symmetry of barium metaborate are also discussed.

Preparation of BaTiO3 by Sol-Gel-Processing

ABSTRACTBarium acetate, titanium ethoxide, and the acetates of calcium and magnesium and zirconium-n-propoxide as additives, were dissolved in an acetic acid methanol mixture. By adding water, this sol was converted to a gel.Extended investigations of the calcination result in a crystalline barium tita-nate without other titanate phases, with a very small amount of carbonate and a negligible contents of free carbon. Aggregates could not be destroyed totally by the milling process. Therefore, the green density of the green bodies reaches only 60 to 65 %. Thus, a minimum sintering temperature of 1200° C was necessary to obtain a density of at least 95 %. In future work, a special treatment to destroy the aggregates must be developed to lower the sintering temperature.

Phase transition at 211 K in crystalline barium nitrite hemihydrate

A phase transition has been observed at 211 K in crystalline barium nitrite hemihydrate by DTA and dielectric measurements. A dielectric relaxation phenomenon was also found and the activation energies governing the relaxation were determined to be 23 kJ mol −1 and 41 kJ mol −1 below and above the transition temperature, respectively. Some discussions have been made on the nature of the phase transition.