A systematic investigation was conducted to evaluate the physical, microstructural and thermal properties of lithium aluminosilicate (LAS) glass-ceramics, with particular emphasis on the effect of MgO concentration on the coefficient of thermal expansion (CTE). Experimental results indicate that the glass to glass-ceramic transformation is accompanied by an approximately 3% volume shrinkage, resulting in an increased density of the glass-ceramic relative to the parent glass. X-ray diffraction analysis confirms the formation of (LiMg,Zn) 1.7 Al 2 O 4 Si 6 O 12 as the main crystalline phase, which is isostructural with the β-quartz solid solution (β-QSS). Transmission electron microscopy reveals uniformly distributed nanocrystals with a mean size of ˜15 nm embedded within the residual glassy matrix. Thermal expansion measurements show that glass-ceramics containing higher MgO exhibit lower CTE values compared to that with lower MgO content, attributed to an increased fraction of the β-QSS phase. Additionally, key thermal characteristic temperatures of the parent glass, including the softening point (T S ), sphere (T SP ), half-sphere (T HSP ), and onset of melting (T M ), were determined using a high temperature heating stage microscope. Such parameters provide valuable insights into the thermal behaviour and processing window of LAS glass-ceramics.

The demand for efficient and durable electrodes at low operating temperatures has driven extensive research in advanced perovskite oxides. In this study, novel cobalt and strontium co-doped neodymium iron oxide (CSNFO) was investigated as a potential electrode material for low-temperature solid oxide fuel cells (LT-SOFCs). The CSNFO composition was synthesized via the glycine-nitrate sol-gel auto-combustion route to ensure uniform cation distribution and controlled particle morphology. Phase formation and structural integrity were confirmed by X-ray diffraction (XRD) analysis, which revealed orthorhombic perovskite structure without formation of secondary phases with crystallite size of 36.46 nm. Field-emission scanning electron microscopy (FESEM) coupled with energy-dispersive spectroscopy (EDX) and High-resolution transmission electron microscopy (HRTEM) confirmed homogeneous elemental distribution and nanocrystalline particle morphology with grain size of 80.6 nm favorable for enhanced electrochemical activity. Electrochemical performance was examined using two different electrolytes, Neodymium Cerium Oxide (NCO) and Yttrium Cerium Oxide (YCO) to compare oxygen ion conductivity over 300–375 ℃, yielding conductivities of 2.01 × 10− 3 and 1.76 × 10− 3 Scm− 1 at 375 ℃. Four-probe DC conductivity measurements for CSNFO showed 26.50 Scm− 1 at 375 ℃, with low activation energy of 0.121 eV. Symmetric cell electrochemical impedance spectroscopy demonstrated thermally activated transport for both CSNFO-NCO and CSNFO-YCO configuration. The CSNFO material possesses promising electrochemical activity and good compatibility with ceria-based electrolytes making it a potential cathode material for LT-SOFCs operating below 400 ℃.

Abstract This study investigates on the synthesis, structural and electrical performance of Sr-doped ceria solid solutions of the composition Ce 0.99 Sr 0.01 O 1.995 , prepared via the conventional solid-state reaction method and sintered at a temperature of 1400 °C to get structural and electrical properties. Both samples were attained relative densities of more than 90%. X-ray diffraction (XRD) analysis confirmed the formation of a cubic fluorite structure. Scanning electron microscopy (SEM) revealed that improved grain packing and reduced porosity in doped samples. Electrical characterization through an A.C. impedance analyzer demonstrated higher the ionic conductivity Ce 0.99 Sr 0.01 O 1.995 than pure CeO 2 . The strontium-doped composition exhibited significantly higher ionic conductivity compared to pure ceria, indicating its potential suitability as an electrolyte material for solid oxide fuel cells (SOFCs).

Ceria has fluorite type crystal structure. The structure can be viewed as an FCC array of Ce ions with the oxygen ions residing in the tetrahedral holes. The 1:2 statiometric is maintained. Pure ceria it shows high electronic conductivity than ionic conductivity. However, the ionic conductivity of ceria based electrolytes can be improved by introducing aliovalent cations to doped ceria.When aliovalant cations (Ca2+,Sr2+,Ba2+,Ln3+,Sm3+,Gd3+,Nd+3) are doped in ceria it shows higher ionic conductivity due to generation of oxygen vacancies in the sub lattice. This paper reports the effect of Ca2+ addition on the structural and electrical properties of Ce0.8Gd0.2O2-\(\delta\)(GDC) electrolyte for low temperature solid oxide fuel cell application. The Ca2+ (0, 0.5, 1 and 2 mol %) doped GDC solid electrolytes have been prepared by solid state method. The sintered densities of the samples are greater than 95%.. Raman spectra show the presence of GDC single phase. AC impedance analysis is used to measure the ionic conductivity of the electrolyte. Among all the compositions, the highest conductivity is observed in the GDC sample with 0.5 mol% Ca2+ addition. Nyquist plots resulted in multiple redoxation process such as grain and grain boundary conductions to final conductivity. The XRD study reveals cubic structure with increase in lattice parameter with Ca2+content in pure GDC electrolyte. It is observed that grain size increases by increasing Ca2+ concentration up-to 1 mol% from 1.72 to 10.20 \(\mu\)m. The GDC electrolyte containing 0.5mol% Ca2+ had an estimated blocking factor that is lower, suggesting that the inclusion of Ca2+ enhanced grain boundary conduction. The Arrhenius plot was used to compute the activation energies, which are in the region of 1eV.

A nanocrystalline solid solution of Ceria co-doped with Samarium, Strontium, and Calcium with composition Ce0.8Sm0.2−x−ySryCaxO2−δ (x = y = 0–0.5) samples pellets were synthesized via solid-state reaction method and sintered at 1300 °C intended to be an electrolyte of IT-SOFC. X-ray diffraction (XRD) confirms the crystalline nature with an fcc fluorite structure. Williamson-hall plots were used to find the microstrain and particle size. Scanning electron microscopy (SEM) was employed for surface morphology with microstructure and found to be nearly spherical particles with porosity, the Energy Dispersive Spectroscopy analysis (EDAX) with color mapping confirmed the stoichiometry. The sample pellets were analyzed using impedance spectroscopy by impedance spectra, where an AC voltage is applied in the range of frequency 1 Hz–10 MHz to record the impedance in the temperature ranging from 300 to 800 °C in the air as a medium. Electrical parameters such as the dielectric constant, ε'r, and AC conductivity, σac have been found. The samples show a negative temperature coefficient of resistance, where the grain boundary conductivity is increased with increasing temperatures showing a peak in the conductivity curve which is also evident from the Nyquist plot for impedance.

Doped ceria based ceramic system is a potential candidate as a solid electrolyte for intermediate or low temperature solid oxide fuel cells. The Gadolinium Doped Ceria (GDC) shows better performance, but the high temperature sintering required for GDC cause cerium ion reduction, which may further enhance electrical conductivity instead of ionic conductivity. This reduction can be lowered by doping GDC system with tri or tetra valent ions. This study emphasizes the preparation and characterization of bismuth and titanium doped GDC system using solution combustion method. Samples with two different dopant concentrations were prepared by the same method and its ionic conductivity is compared. Both the samples show fluorite structure under X-ray diffraction analysis and the micrographs are agglomerated with less voids in them. The Raman and X-ray Photoelectron Spectroscopy results confirm the presence of oxygen vacancies in the prepared samples. The impedance spectroscopy study shows that the sample with low dopant concentration has better ionic conductivity of the order of 10− 3 S/cm. The applications of SOFC, especially as an auxiliary power unit that supports batteries in electric vehicles will help to reduce the use of combustion engine vehicles in everyday life, which further reduces environmental pollution.

The gadolinium-doped nickel ferrites with the chemical composition of NiFe2−xGdxO4 (0.00 £ x £ 0.25) ferrites were synthesized by sol–gel auto-combustion. Spinel ferrite phase formation was analyzed using XRD analysis. The dielectric constant, loss tangent, and the AC conductivity were investigated. The dielectric properties with Gd doping content were studied from 100 Hz to 1 MHz frequency range from room temperature to 400 °C. These results were very well in agreement with Maxwell–Wagner interfacial polarization. The dielectric properties were observed to depend on the frequency and the Gd doping concentration. According to Koop theory, spinel ferrites exhibit a beneficial trend whereby their dielectric constant drops as frequency increases. This behavior is supported by the various cationic distributions within the spinel structure. The use of these materials in medium-frequency devices is reflected in the largest magnitude of the tangent loss at low frequencies. Thus, projected spinel nanoferrites could be advantageous for microwave and sophisticated electronics devices.

Lithium Aluminosilicate glass-ceramics with striae (LAS-WS) and without striae (LAS-WoS) were processed using melt casting technique. LAS-WS and LAS-WoS samples were characterized and found stress birefringence >10 nm/cm and <10 nm/cm, respectively. LAS-WS and LAS-WoS samples were subjected to structural, microstructural, high temperature dielectric and electrical characterization. The presence of striation did not significantly affected the formation of β-spondumene structure during crystallization heat treatment. TEM image confirms the formation of nanocrystals in the glass matrix of lithium aluminosilicate glass-ceramics. The homogeneous distribution of LAS nanocrystals of average size of 3-6 nm is evident from TEM results. Stress birefringence distribution in lithium aluminosilicate glass-ceramic clearly shows the striae formation. Shadowgraphy images confirmed the striae free and striae containing regions in the glass-ceramic. The effect of striae on dielectric properties and AC conductivity was analysed using impedance spectroscopy and it was found that the value of the relative permittivity decreased from 415 (1.2 Hz) to 9.76 (1.2 MHz) for LAS-WoS and from 401 (1.2 Hz) to 10.3 (1.2 MHz) for LAS-WS, respectively. It was found that striae in LAS glass-ceramics influence the electrical impedance and AC conductivity relaxation process rather than relative permittivity. The effect of striae on crystallization and morphology are presented. Both the samples have shown crystallinity of more than 75%. The electrical conductivity of σ=2.0 x 10-3 S/cm for LAS-WoS and 2.7x10-3 S/cm for LAS-WS at 300 oC as well as σ=4.6 x 10-3 S/cm for LAS-WoS and 6.9x10-3 S/cm for LAS-WS at 700 oC are found to be in good agreement due to increase in the electrical conductivity with temperature. The ionic conductivity of the material due to Li-ion mobility with respect to temperature and electric field and possible mechanism of AC conductivity are discussed. The results presented indicates the potential application of this material that demands high temperature operation of lithium aluminosilicate glass-ceramics.

Lithium Aluminium Silicate (LAS) samples were fabricated through a melt casting process using Lithium carbonate, Aluminium hydroxide, Silica and other additives as raw materials. The melt was drain casted at 1300 degrees C in a pre-heated mould followed by annealing and ceramization at 850 degrees C. Ceramized samples were subjected to X-ray diffraction. The density of the samples was found to be in the range of 2.53-2.54 g/cm3. The sample was found free from bubbles and inclusions after optically polishing. Mechanical properties including hardness, flexural strength, fracture toughness and compressive strength of LAS samples were evaluated. Knoop hardness of the LAS samples was found to be 597-669 kg/mm2. LAS sample exhibited a peak flexural strength of 110-114 MPa and compressive strength of 221 MPa before fracture. Additionally, the total fracture energy release rate (Jc) of LAS samples along with R-curve and fractography were also studied. R-curve exhibited an increasing trend of Jc with respect to normalised displacement without any sign of saturation indicating the scope for optimisation of quantification of crystals fraction in the glass matrix to obtain the predominant toughening behaviour. Finally, the physico-chemical, microstructural and optical properties were measured and correlated with the mechanical properties observed. Near to theoretical density, high crystallinity and superior mechanical properties of processed LAS glass-ceramic can be used in strategic and civilian applications.

The present study examines the interfacial effect on the area-specific resistance (ASR) offered by SrM0.1Mo0.9O3-delta (M = Mg2+, Fe3+)/Gd0.1Ce0.9O2-delta (GDC) composite electrodes. The symmetrical cells having 8YSZ electrolyte and SrFe0.1Mo0.9O3-delta/Gd0.1Ce0.9O2-delta composite electrodes are fabricated with and without the GDC buffer layer. The electrode ASR in cells with and without GDC-buffer layer is 0.09 O.cm2 and 0.68 O.cm2 at 850 degrees C in 3% H2O/H2, respectively. More than a 50% rise in the magnitude of electrode ASR is seen in cells with no GDC buffer layer after 10 redox cycles. Phase analysis of these cells reveals a dense layer of an insulating SrZrO3-based phase formed at the electrode/electrolyte interface due to the chemical reaction between SrFe0.1Mo0.9O3-delta and 8YSZ. In contrast, the cells possessing a GDC buffer layer show a small ASR increase from 0.09 O.cm2 to 0.14 O.cm2 after the same number of redox cycles without the presence of any secondary phase. The effect of the current collector contact area on the ASR of the SrMg0.1Mo0.9O3-delta/Gd0.1Ce0.9O2-delta composite electrode is also evaluated. Symmetrical cells with a dense GDC buffer layer and composite electrodes are prepared. The Pt current collector area on the electrode layer is varied from 0.13 cm2 to 0.5 cm2, and the electrode specific resistance is measured at 850 degrees C in a 3% H2O/H2 environment. The electrode resistance declines with increasing current collector area. The cell with the electrode surface entirely covered by the current collector exhibits a very low ASR of - 0.07 O. cm2. The sensitivity of the interfacial polarization resistance towards a slight change in the strength of the current field is the possible reason for observing such ASR variation.

In this work, the hydrothermal synthesis of cobalt-doped tin selenide (SnSe) is reported. The phases of the samples were obtained as single phase using X-ray diffraction. 3D flower-like morphology is revealed up to x = 0.05 of Co, and thereafter, they transformed into a rod-like shape for higher concentrations as revealed by scanning electron microscope. The temperature-dependent dielectric properties and electrical modulus studies were investigated in a frequency range of 100 Hz–12 MHz for temperatures 323–523 K. Large values of dielectric constant (of the order of 108–109) in the low-frequency region and small values of dielectric constant (ε' ≈ 50–1400) in the high-frequency region are obtained at various temperatures for Co-doped SnSe. The temperature dependence of frequency exponent ‘s’ indicates that the correlated barrier hopping is the probable mechanism for the hopping of charge carriers. The responses in the dielectric studies show the applications of the material in microelectronic and dielectric device applications.

Transparent MgAl2O4 spinel ceramic parts were fabricated by the slip casting process and densified to > 99

In our current study, we have investigated the effect of potassium doping on AC conductivity and the dielectric properties of tin selenide (SnSe). Potassium-doped SnSe (KxSn1-xSe with x = 0–20 mol%) polycrystals were synthesized via hydrothermal method. The phase of the synthesized samples was confirmed to be single phase with orthorhombic structure as obtained by X-ray diffraction. The average crystallite size for all the KxSn1-xSe samples was calculated using the Debye–Scherrer formula and they were found to be decreased as potassium (K) concentration increased. Scanning electron microscope revealed plate-like morphology for all KxSn1-xSe samples. Transmission electron microscope studies at high resolution showed plate-like morphology which is connected with small nanorods for the K0.20Sn0.80Se. Optical studies were carried out using UV–Vis–NIR diffuse reflectance spectroscopy. The bandgap values were found to be decreased as K concentration is increased. Temperature-dependent dielectric studies were studied for all KxSn1-xSe samples. Correlated barrier hopping is responsible for the transport of charge carriers in the conduction mechanism. Electrical modulus studies reveal a non-Debye-type dielectric relaxation phenomenon. The results of dielectric studies specify the application of K-doped SnSe in frequency related and capacitive storage devices.

Doping can induce and tune many physical properties of a semiconductor host lattice. Here, we report the effect of cobalt doping on optical, dielectric, and magnetic properties of SnSe. We have synthesized Cobalt doped SnSe (CoxSn1-xSe) polycrystals with x = 0.00, 0.01, 0.03, 0.05, 0.10 and 0.20 using hydrothermal method. The single-phase was confirmed from X-ray Diffraction. Morphology of CoxSn1-xSe polycrystals was examined through Scanning Electron Microscope and it revealed a 3D flower-like morphology for undoped and CoxSn1-xSe till x = 0.05. The morphology changed to rod-like shapes for higher compositions of Co. The bandgaps of CoxSn1-xSe were reduced as determined from UV-Vis-NIR Diffuse Reflectance Spectroscopy. Dielectric properties of the samples were studied at room temperature in a frequency range from 100 Hz to 12 MHz. Vibrating Sample Magnetometer studies revealed the ferromagnetism for all the samples at room temperature. The results indicate the possible applications of the material in spintronic devices.

Pressure Slip Casting (PSC) using polymer moulds offers several advantages over Conventional Slip Casting (CSC) of ceramics such as enhanced productivity in combination with higher green density, homogeneity and low rejections. PSC is currently practiced in table-ware industries however, application to the technical ceramics is limited owing to the collapse of cast part while de-moulding during pressure cast cycle under pneumatic pressure. Current study focuses on this key issue and demonstrated pressure casting process successfully for the fabrication of alumina parts. Slips of a mixture of alumina with different particle sizes in the various proportions and solid loadings were prepared. Slip under PSC resulted in effective interlocking of the particles retaining the shape while de-moulding and achieved a sintered density of 98.6% of theoretical density (TD). Slurry on CSC exhibited a lower sintered density of 97% of TD. Selection of particles with sizes in optimised proportion for PSC results in effective interlocking of particles in green parts as well as grains on sintering as revealed by the microstructure. This leads to higher density and mechanical properties. Slip thus optimised were shaped into solid spheres of ϕ 60 mm by PSC targeting grinding applications.

The electrochemical performance of porous composites of Gd0.1Ce0.9O2-delta/SrMg0.1Mo0.9O3-delta is investigated for the anode application under a typical fuel environment of solid oxide fuel cells (SOFCs). Nanosized powder of SrMg0.1Mo0.9O3-delta possessing a cubic perovskite phase is synthesized using the solution-combustion method. Composites having the composition of xGd(0.1)Ce(0.9)O(2-delta)/SrMg0.1Mo0.9O3-delta (where x is a weight fraction of Gd0.1Ce0.9O2-delta ranging from 0.5 to 0.8) are prepared using a traditional mixing method. At 850 degrees C, the DC electrical conductivity of SrMg0.1Mo0.9O3-delta under moist 20% H-2/N-2 is 617 S.cm(-1) which declines to similar to 105 S.cm(-1) for 0.6Gd(0.1)Ce(0.9)O(2-delta)/SrMg0.1Mo0.9O3-delta. Symmetric cells are fabricated using dense disks of yttriastabilized zirconia as an electrolyte with a thin Gd0.1Ce0.9O2-delta buffer layer coated on both faces. An optimized slurry of the composite electrode is blade-coated on the dense buffer layer and subsequently sintered at 950 degrees C in air. Scanning electron microscopy reveals a porous microstructure with an electrode layer thickness of similar to 14 mu m. A single-phase SrMg0.1Mo0.9O3-delta electrode exhibits an area-specific resistance of 0.28 Omega.cm(2), which is less than 6 times the value offered by undoped SrMoO3 at 800 degrees C in 3% H2O/H-2. The optimum Gd0.1Ce0.9O2-delta addition (x = 0.7) to SrMg0.1Mo0.9O3-delta resulted in a significantly low area-specific resistance of 0.09 Omega.cm(2) at 800 degrees C. The performance of the optimized electrode composite is also evaluated by modifying the microstructure of the Gd0.1Ce0.9O2-delta buffer layer. Interestingly, the symmetrical cell with a porous buffer layer further reduces the electrode area-specific resistance to 0.065 Omega.cm(2). The observed results are ascribed to the penetration of electrocatalyst SrMg0.1Mo0.9O3-delta particles inside the porous buffer layer during the blade-coating. This possibly extends the triple-phase boundary length and facilitates the charge-transfer reaction. The electrochemical performance attained in the present study is far superior to the other Ni-free ceramic anodes reported earlier, which highlights the promise of 0.7Gd(0.1)Ce(0.9)O(2-delta)/SrMg0.1Mo0.9O3-delta for the SOFC anode.

Recently, tin selenide has attracted vast research interest in many fields due to its unique properties. Here, Na-doped SnSe polycrystals were successfully synthesized using hydrothermal method. Single phase was exhibited by all the samples as revealed from X-ray diffraction (XRD). Scanning electron microscope (SEM) studies for undoped SnSe showed a 2D plate-like morphology and converted it into 3D flower-like morphology with increasing Na concentration. The optical bandgap values obtained using UV–VIS–NIR diffuse reflectance spectroscopy were found to decrease with increasing Na concentration. Dielectric and electrical modulus studies were carried out in the frequency range from 100 Hz to 10 MHz for temperatures from 323 to 523 K. Correlated barrier hopping (CBH) is a probable mechanism for the charge carriers in all the compositions of NaxSn1−xSe. The electrical modulus studies indicated an incomplete dielectric relaxation of the non-Debye type. The high values of the real part of permittivity and AC conductivity for the Na0.20Sn0.80Se sample have potential applications as capacitive energy-storage devices.