Ceramic based barium strontium titanate (BST) solid solutions with the formula Ba1 − xSrxTiO3 are very important candidates for a wide range of device applications. Several doped (Mn and Mg) and undoped samples were prepared by standard solid-state reaction. Special emphasis was put on compositions with x = 0.35 and 0.60, with high potential for applications. The samples were sintered at temperatures in the 1200 ÷ 1260 °C range. Structural X-ray diffraction analysis preformed confirms the perovskite structure. The dielectric parameters were investigated in a wide temperature range between − 150 and 150 °C. The temperature was cyclically changed in both directions, up and down, at a rate of less than 2 °C/min. Both permittivity and dielectric loss were measured at low frequencies, 1 kHz. The peak values of the permittivity are increasing from 2000 to 4000 with the sintering temperature increase. Moreover the dielectric parameters were measured at room temperature in microwave domain (1 ÷ 2 GHz). The Curie temperature of BST samples with x = 0.35 and x = 0.6 is in agreement with the Curie point dependence on Sr content, as we have previously reported. 相似文献
Nanocrystalline and well dispersed barium strontium titanate (BST) powders were prepared by a novel and simple citrate precursor method. This method involved direct crystallization of a white precursor from a stable solution in the citric acid (CA)–ethylene glycol (EG)–tetrabutyl titanate–M2+ (M = Ba, Sr) system under a specific pH value range. Subsequent heat treatment of the precursor at 850 °C led to a pure phase BST powder. TG/DTA was used to examine the decomposition behaviour of the precursor. The crystalline phase and morphology of the BST powders were investigated by XRD and TEM. It was found that the BST powders synthesized by citrate precursor process were more homogeneous and uniform than that obtained by the citrate gel method. 相似文献
We propose an innovative idea to bond the dielectric barium strontium zirconium titanate (BSTZO) plates with magnesium oxide (MgO) as the spacers to achieve a hermetic module without any air gaps between the dielectric and the spacer. The gold metallization can be applied across the whole assembly to create an integrated electrode. The gold metallization also eliminates pressure contact by external copper plates assemblies, which are required to achieve good contacts between the copper plates and the metallized surfaces of the BSTZO. The MgO spacers are processed using a dry-pressing and pressureless-sintering method. The thermal expansion coefficient (CTE) of BSTZO and MgO spacer was measured. In addition to matching the CTE between BSTZO dielectric and the MgO spacer, it is also critical to develop a good bonding material with CTE matching to BSTZO and MgO spacer. The effect of CTE for various bonding compositions on the dielectric properties was thoroughly studied and reported. The mechanism explaining the high and low dielectric constants for the laminates is proposed and discussed based on the CTE results and their effect on microstructural development. 相似文献
The sol–gel method was used to synthesize two different Ba0.75Sr0.25Ti0.95Zr0.05O3 powders: one of high purity and the other of low purity. These two sol–gel-synthesized powders show two distinct particle sizes and surface areas. The slip casting method was applied to these two sol–gel powders followed by a pressureless sintering, which shows large differences in sintered density and grain size for the pressureless sintered disks. Neutron powder diffraction shows a transition to the nonpolar cubic Pm–3m space group at higher temperatures for both materials. Pair distribution function analysis was used to examine the local displacements of the Ti4+ and Zr4+ cations. The dielectric constant, loss tangent, and bias were measured on these two materials. 相似文献
Ferroelectric barium titanate nanoparticles (BTO NPs) may play critical roles in miniaturized passive electronic devices such as multi-layered ceramic capacitors. While increasing experimental and theoretical understandings on the structure of BTO and doped BTO have been developed over the past decade, the majority of the investigation was carried out in thin-film materials; therefore, the doping effect on nanoparticles remains unclear. Especially, doping-induced local composition and structure fluctuation across single nanoparticles have yet to be unveiled. In this work, we use electron microscopy-based techniques including high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), integrated differential phase contrast (iDPC)-STEM, and energy dispersive X-ray spectroscopy (EDX) mapping to reveal atomically resolved chemical and crystal structure of BTO and strontium doped BTO nanoparticles. Powder X-ray diffraction (PXRD) results indicate that the increasing strontium doping causes a structural transition from tetragonal to cubic phase, but the microscopic data validate substantial compositional and microstructural inhomogeneities in strontium doped BTO nanoparticles. Our work provides new insights into the structure of doped BTO NPs and will facilitate the materials design for next-generation high-density nano-dielectric devices.
Barium strontium titanate (BST) with the molar formula (Ba0.8Sr0.2TiO3) has been prepared by two different processing methods: mixed-oxide (BST-MO) and reaction-sintering (BST-RS). X-ray powder diffraction study shows differences in grain size and crystal symmetry for both these ceramics. The former shows a tetragonal symmetry while the latter presents a cubic symmetry. The occurrence of polar micro-regions associated with the higher chemical non-homogeneous distribution of ion defects from the influence of the processing parameters is the main reason for the higher peak dielectric constant (Km), the higher remanent polarization (Pr), the higher coercive field (Ec), the higher peak current density (Jm), and the lower temperature of peak dielectric constant (Tm) in BST-MO ceramics. 相似文献
Ba0.6Sr0.4TiO3 (BST) nanopowders have been prepared using the modified citrate method with ammonium nitrate as a combustion promoter, and the formation mechanism, phase evolution, and particle size have been investigated using TG/DTA, XRD, and SEM. It is found that the peaks of barium carbonate disappear when the precursor powders are calcined at 650 °C. The fine particles of the nanopowders calcined with the combustion promoter addition are homogeneous and well-dispersed and their narrow size distribution is about 60-90 nm. Comparatively, the particles of the powder calcined without the ammonium nitrate addition are inhomogeneous, with an evident agglomeration. The mechanism for the above results is attributed to that a reaction can generate soft and loose precursor powders by the adoption of ammonium nitrate, and hence a pure BST phase could occur at the low synthesis temperature of 650 °C. 相似文献
The barium titanyl oxalate, which was the precursor of barium titanate, was prepared by homogeneous precipitation using the diethyl oxalate as a precipitating agent. The oxalate dried at 80 °C was the crystalline phase, which was converted to amorphous-like phase after drying at 120 °C. The weight loss of oxalate was 47.3 wt%. The chemical formula of the oxalate could correspond to BaTiO(C2O4)2 · 4H2O. The barium titanate obtained from the calcination of oxalate at 850 °C was a tetragonal phase with a particle size of 0.2 m. 相似文献
A system of barium strontium titanate glass ceramics with different fluoride concentrations were prepared by melt-annealing technique. The effect of fluoride doping on impedance spectra of the barium strontium titanate glass ceramics were investigated. According to the impedance spectroscopy studies, three (low, middle, and high frequency) electrical responses, which corresponds to glass phase, crystal–glass interface and crystal interior were identified. It is shown that with the increase of fluoride concentration, the resistivity of the glass phase passed through a minimum and then increased. In addition, the capacitance of the crystal–glass interface increased and the capacitance of the crystal phase decreased with the increase of the fluoride concentration. Moreover, as a result of ac conductivity calculation and analysis, it is believed that the dc conduction was affected by the glass and crystal–glass interface regions and ac regime was attributed to the crystal phase. Based on the results, a change of the compensation mechanism from electronic to ionic one with variation in fluoride concentration was proposed. 相似文献
A novel modified chimie douce synthetic approach based on the gel to crystallite conversion (G–C) method has been developed to prepare strontium titanate SrTiO3, strontium stannate SrSnO3, and mixed strontium stannate–titanate SrSn1−xTixO3 (x = 0.05–0.5). The obtained materials were characterized by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The formation of fully crystalline SrTiO3 was observed in the temperature range of 800–1000 °C. The formation of monophasic SrSnO3 occurs in the temperature range of 700–900 °C. At lower and higher temperatures the formation an impurity phases such as SrCO3 and SnO2 takes place. The same synthetic approach has been applied for the preparation of mixed strontium stannates–titanates SrSn1−xTixO3. The SEM images of SrTiO3 samples indicated that the powder particles are 1–5 μm in size having approximately plate-like shape. Quite different surface morphology was determined for SrSnO3 samples revealing the size of crystals from 500 nm to 40 μm. For the composition with x = 0.15, it was observed that the grain growth is uniform and the size of the grains is of the order of ∼2–5 μm. 相似文献
A microstripe cavity was used to make microwave (f∼10 GHz) measurements of the time of variation of the permittivity of SrTiO3 and (Ba,Sr)TiO3 films exposed to unipolar video-frequency voltage pulses. It was shown that the permittivity of SrTiO3 films varies over times less than 30 ns. For (Ba,Sr)TiO3 films two characteristic times of variation of the permittivity were identified: a fast variation over times less than 30
ns and a slower variation, on the order of 20 μs.
Pis’ma Zh. Tekh. Fiz. 24, 19–25 (October 12, 1998) 相似文献
Barium strontium titanate with Ba/Sr ratio of 50/50 (BST5) was prepared using a modified polymeric precursor method. Unlike
other methods, it proved to be cost effective since neither moisture sensitive nor costly starting materials were used for
the preparation. The optimum preparation condition was established, and it was found that an annealing temperature of 600 °C
with a dwell time of 20 h followed by a heat treatment at 800 °C with dwelling time of 4 h is enough to obtain well crystallized,
phase pure fine powder of BST5. The oxide powder thus obtained was single phased, crystalline with cubic structure. The average
lattice constant of the polycrystalline oxide was examined using XRD and it was determined to be 0.3950 nm (±0.0003 nm). The
average crystallite size of the ceramic was found to be about 25–30 nm. The reaction pathway, temperature of decomposition
of the precursor and the temperature of formation of the oxide was found using the data from the EGA-TGA-MS coupled instrument.
TGA data showed about 75% of total weight loss over the entire heating process. The SEM studies showed that the grains were
in micrometer size range, having high degree of agglomeration and irregular morphology. This process is interesting as it
yields phase pure BST5 ceramic at a temperature of 800 °C devoid of secondary phases like (Ba,Sr)2TiO4. 相似文献