J. Appl. Cryst.の発刊に際して

Fundamentals of ceramic powder processing and synthesis

Material science. A. E. Leikin and B. I. Rodin

Among n-type oxide thermoelectrics, donor-substituted strontium titanates, prepared in highly reducing conditions, show a particularly attractive thermoelectric figure of merit. High electrical conductivity, combined with outstanding redox tolerance and perovskite-phase stability of these materials, also make them prospective candidates for solid oxide fuel cell (SOFC) anode components. This work represents a first attempt to process strontium titanate ceramics with significant W for Ti substitution and to assess their relevant defect chemistry-related aspects and electrical and thermal properties, seeking mainly highly performing oxide thermoelectrics. Combined XRD/XPS/SEM/EDS studies of SrTi1–xWxO3±δ (x = 0.01–0.10), prepared by a conventional solid state route, demonstrated that the maximum solubility of tungsten corresponds to 3–5% mol, depending on firing conditions and other composition changes. Separation of tungsten-containing phases on a submicro- and nanoscale level and formation of core–shell m...

Design of SrTiO3-Based Thermoelectrics by Tungsten Substitution

The polycrystalline sample of K2Pb2Dy2W2Ti4Nb4O30 was synthesized by high—temperature solid—state reaction method (calcinations temperature ~1,050 °C and sintering temperature ~1,075 °C). The phase formation of the desired compound was confirmed by preliminary X-ray structural analysis. The scanning electron micrograph shows uniform plate and rod like grain distribution throughout the surface of the sample without much pores. Detailed studies of the nature of (1) variation of dielectric parameters with temperature (27–480 °C) and frequency (1 kHz–5 MHz) and (2) polarization (at three different temperatures) confirmed the existence of ferroelectricity in the material, with phase transition occurring at 316 °C. The temperature dependence of electrical parameters (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation between its micro-structure (i.e., bulk, grain boundary, etc.) and electrical properties. The nature of temperature dependent dc conductivity follows the Arrhenius equation, and reveals the negative temperature coefficient of resistance (NTCR) behaviour of the material. The material obeys Jonscher’s universal power law which is evident from the graphs of frequency dependence of ac conductivity.

Structural, dielectric and electrical properties of dysprosium based new complex electroceramics

Barium titanate is used as material for many important and widely used ceramic components and devices such as high permittivity ceramic capacitors, piezoelectric ceramic transducers and thermisters with positive temperature coefficient of resistivity (PTCR) [1, 2, 3, 4]. Samples of compositions BaTi 1 − x W x O 3 ; x = 0.0, 0.15 were prepared by solid-state reaction technique using high purity oxides/carbonates. The samples were calcined at 1150°C for 2 hrs and sintered at 1200°C and 1300°C for 2 hrs. XRD diffroctgrams show that a single phase layered perovskite structure is formed in the samples. Lattice parameters and tetragonal strain (c/a) are observed to decrease in the substituted sample. Dielectric constant and dielectric loss have been measured as a function of temperature and frequency. The variations of dielectric constant (ϵ r ) with temperature at various frequencies show that the compounds undergo a diffuse type ferro—paraelectric phase transition. Curie temperature is observed to decrease fr...

Effect of W Substitution on Structural, Dielectric and Electrical Properties of BaTiO3 Ferroelectric Ceramics

Aurivillius type bismuth layered materials have received a lot of attention because of their application in ferroelectric non-volatile random access memories. Among bismuth layer structured ferroelectric ceramics SrBi2Ta2O9 (SBT)/SrBi2Nb2O9 (SBN) are of great interest for researchers because of their fatigue resistance and less distorted structure. Recently vanadium substitution in SBN/SBT has shown interesting electric and dielectric properties. In the present work, processing conditions, microstructure and electrical studies of vanadium doped SBN ferroelectric ceramics have been performed. Samples of compositions SrBi2V
 x
 Nb2-x
 O9, x = 0.0, 0.1, 0.3, 0.5 were prepared by solid-state reaction technique using high purity oxides / carbonates. The samples were calcined at 700 °C and sintered at 800 °C. X-ray diffractograms show that a single phase layered perovskite structure is formed in all the samples. Effect of partial substitution of pentavalent niobium ion (0.68 A) by smaller pentavalent vanadium ion (0.59 A) at B site on the microstructure, Curie temperature, Dielectric constant, Dielectric loss and electrical conductivity have been investigated. Dielectric properties of SBVN have been investigated from room temperature to 500 °C and frequency of 100 Hz to 1 MHz. Dielectric constant values at their respective Curie points are observed to increase with increasing vanadium concentration. Curie temperature is observed to be maximum in x = 0.1 vanadium doped sample. Strong relaxor like dielectric relaxation at the transition temperatures have been observed. With increasing vanadium concentration the dielectric loss is observed to increase significantly. It is also observed that dielectric loss increases with increase in temperature. The variation of conductivities in these samples is also reported.

Structural and electrical properties of SrBi2VxNb2−xO9 ferroelectric ceramics: Effect of temperature and frequency

In the present work, samples of compositions SrBi 2 Nb 2 O 9 and SrBi 2 Nb 1.9 Mo 0.1 O 9 were prepared by solid state reaction method. X ray diffraction analysis reveals the formation of single phase perovskite structure. Although the perovskite structure of SBN is retained but slight change in the lattice parameters is observed. Dielectric constant and dielectric loss have been measured as a function of temperature (300 K–800 K) and frequency (1 kHz, 10 kHz and 100 kHz). Peak Dielectric constant is observed to increase from 465.05 for pure SBN to 613.17 for molybdenum substituted SBN while Curie temperature is observed to decrease from 420°C for pure SBN to 365°C for molybdenum substituted SBN. Dielectric loss is observed to increase from 0.066 for pure SBN to 0.123 for the doped sample at their respective Curie temperature. P-E loops have been recorded and retentivity and coercevity have been determined. The coercive field and remanant polarization values are observed to decrease from 10.647 μzv/c.m. a...

Structural, Dielectric and Ferroelectric Studies of Molybdenum Substituted Sr2Bi2Nb2O9 Ferroelectric Ceramics

In the present work, samples of compositions BaTi1?xWxO3; x= 0.00 and 0.15 were synthesized by solid-state reaction technique at various sintering temperatures of 1200°C, 1250°C and 1300°C and durations 2hr and 5hr. The X- ray diffractograms analyses reveal the formation of the samples having single phase crystalline structure. Tetragonal strain of the samples has been calculated and its variations with sintering temperature and duration have been studied. Particle size of the studied samples has been found to change with sintering temperature and duration. Dielectric properties of the samples have been studied as a function of temperature and frequency. The variation of dielectric constant (?r) with temperature shows that the samples undergo a diffuse type ferro - paraelectric phase transition. The dielectric constant is found to increase with increasing temperature and duration. Variation of dielectric loss (tan?) with temperature have also been measured. Further, diffusivity of the samples have been calculated and is reported in this paper.

Effect of sintering temperature on dielectric properties of tungsten doped barium titanate

Samples of compositions SrBi2VxNb2?xO9, x = 0.0, 0.1, 0.3, 0.5 were prepared by solid-state reaction technique using high purity oxides/carbonates. The samples were calcined at 700°C and sintered at 900°C. XRD diffractograms show that a single phase layered perovskite structure is formed in all the samples. Effect of partial substitution of pentavalent niobium ion (0.68A°) by smaller pentavalent vanadium ion ( 0.59A°) at B site on the microstructural, Curie temperature, dielectric constant and dielectric loss have been investigated. Partial substitution of Nb5+ by V5+ is observed to have a profound effect. Dielectric properties of SBVN were investigated from room temperature to 500 °C and frequency of 100 Hz to 1 MHz. Dielectric constant values at their respective Curie points are observed to increase with increasing vanadium concentration. An overall increase in Curie temperature is also observed with increasing vanadium concentration. Strong relaxor like dielectric relaxation at the transition temperature have been observed. With increasing vanadium concentration the dielectric loss is observed to increase significantly. It is also observed that dielectric loss increases with increase in temperature.

Sameer Jain

Papers

Effect of W Substitution on Structural, Dielectric and Electrical Properties of BaTiO3 Ferroelectric Ceramics

Structural and electrical properties of SrBi2VxNb2−xO9 ferroelectric ceramics: Effect of temperature and frequency

Structural, Dielectric and Ferroelectric Studies of Molybdenum Substituted Sr2Bi2Nb2O9 Ferroelectric Ceramics

Effect of sintering temperature on dielectric properties of tungsten doped barium titanate

Synthesis and characterization of vanadium doped SrBi2Nb2O9 ferroelectric ceramics