Arun Kumar Yadav

Structural and ferroelectric properties of perovskite Pb(1−x)(K0.5Sm0.5)xTiO3 ceramics

PbTiO3 has the highest tetragonal distortion (c/a ∼ 1.064) and highest spontaneous polarization among perovskite titanates. But, it is hazardous and hence one needs to reduce Pb content by substituting or reducing Pb content for use in practical applications. Pb(1−x)(K0.5Sm0.5)xTiO3 (0 ≤ x ≤ 0.5) perovskite powders were synthesized by sol–gel process, where Pb2+ was replaced by a combination of K0.51+Sm0.53+ (equivalent charge and comparable ionic radius) providing an excellent substitution model to study changes in structural and electrical properties. Vibrational properties and dielectric properties are modified with substitution. A polar tetragonal to a nearly nonpolar cubic phase transition decreases to lower temperatures with substitution due to the reduction of the lattice strain with substitution. Ferroelectricity is retained even for x = 0.5, which has a nearly cubic phase and makes the material technologically important.

Structural and dielectric properties of Pb(1−x)(Na0.5Sm0.5) x TiO3 ceramics

A correlation between structure and vibrational properties related to a ferroelectric to paraelectric phase transition in perovskite Pb(1−x)(Na0.5Sm0.5)xTiO3 (0u2009≤u2009xu2009≤u20090.5) (PNST-x) polycrystalline powders is discussed. Substitution leads to reduction of tetragonality which is associated with a shift of the phase transition to lower temperatures. The nature of the phase transition gets diffused with increasing substitution.

Investigation of La and Al substitution on the spontaneous polarization and lattice dynamics of the Pb(1-x)LaxTi(1-x)AlxO3 ceramics

The phase purity and crystal structure of PLTA samples (synthesized via sol-gel process) were confirmed using synchrotron x-ray powder diffraction (wavelength, lmbda= 0.44573 A. Rietveld analyses of powder x-ray diffraction data confirmed the tetragonal structure for compositions with more than 0.18 and cubic structure for the sample with 0.25 composition. Temperature-dependent XRD was performed to investigate the structural change from tetragonal to cubic structure phase transition. Raman spectroscopy at room temperature also confirmed this phase transition with composition. Field emission scanning electron provided information about surface morphology while an energy dispersive x-ray spectrometer attached with FESEM confirmed the chemical compositions of samples. Temperature and frequency dependent dielectric studies showed that the tetragonal to cubic phase transition decreased from 680 K to 175 K with the increase in the x from 0.03 to 0.25, respectively. This is correlated with the structural studies. Electric field dependent spontaneous polarization showed proper ferroelectric loop for 0.06 to 0.18 belonging to a tetragonal phase while after 0.25 composition the spontaneous polarization vanishes.Bipolar strain versus electric field revealed a butterfly loop for 0.06 to 0.18 compositions. Energy storage efficiency initially increases nominally with substitution but beyond 0.18 composition enhances considerably.

Sol–gel synthesis and characterization of a new four-layer K0.5Gd0.5Bi4Ti4O15 Aurivillius phase

Monophasic K0.5Gd0.5Bi4Ti4O15 powders were synthesized via a citrate-based sol–gel route. Rietveld analysis of powder X-ray diffraction data confirmed the composition to be a pure four-layer Aurivillius phase with an orthorhombic structure (space group A21am and unit cell parameters au2009=u20095.42798(52)xa0Å, bu2009=u20095.41821(41)xa0Å, and cu2009=u200941.2723(33)xa0Å) at room temperature. The chemical composition and the morphology of the sintered pellets were examined by field emission scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). The dielectric properties were investigated as a function of temperature (27–600u2009°C) at various frequencies (10xa0Hz–1xa0MHz), and the phase transition was observed at 560u2009°C. Ferroelectric nature of K0.5Gd0.5Bi4Ti4O15 was demonstrated by the polarization–electric field (P–E) hysteresis loop. Equivalent circuit modeling of the complex impedance data was employed to determine the conduction behavior. The temperature dependence of dc conductivity was found to follow the Arrhenius law associated with the activation energy of 1.22u2009±u20090.02xa0eV and was attributed to the long-range movement of oxygen vacancies.

Lead free dielectric ceramic with stable relative permittivity of 0.90(Na0.50Bi0.50Ti)O3-0.10AgNbO3

Structural, dielectric and ferroelectric properties in perovskite 0.90(Na0.50Bi0.50Ti)03-0.10AgNb03 polycrystalline powders prepared by sol-gel method are discussed. Diffuse phase transition and new type of dielectric anomaly was observed with highly steady capacitive properties in the 135-450 °C temperature range. This compound shows remarkable dielectric with dielectric constant er ~ 1000 with a variation of ± 7% and tan δ = 0.004~0.25 in 135- 450 °C temperature. In addition, it also showed excellent ferroelectric properties with saturation polarization Ps = 13.5 μC/cm2, remnant polarization of Pr = 7.6 μC/cm2 and a low coercive field Ec = 36 kV/cm at room temperature. Stable dielectric constant (er) and low dielectric loss (tan δ) in a wide temperature range observed for the titled composition makes it an interesting candidate for potential use in fast growing “high-temperature electronics” industry applications.

Size and strain dependent anatase to rutile phase transition in TiO2 due to Si incorporation

Powders with compositions Ti(1−x)SixO2 (where 0u2009≤u2009xu2009≤u20090.25) were prepared to systematically study the effects of Si doping on anatase to rutile phase transformation. Samples were synthesized using a modified sol–gel route and were heat treated at various temperature in 450–950xa0°C range. XRD, Raman Spectroscopy, UV–vis spectroscopy, SEM, TEM were used to study the effects of dopant concentration and heat-treatments on the crystal structure, crystallite size and particle size. Rutile phase was found to occur only above a critical crystallite size. Si doping was found to delay the onset of anatase to rutile phase transformation from 500xa0°C (for composition xu2009=u20090) to 800xa0°C (for xu2009=u20090.25) through the lattice strain and crystallize size modification. Interplay between the average crystallite sizes, lattice strain, annealing temperature, and their effect on phase transition are discussed in terms of Si incorporation in lattice.

Increase in depolarization temperature and improvement in ferroelectric properties by V5+ doping in lead-free 0.94(Na0.50Bi0.50)TiO3-0.06BaTiO3 ceramics

A detailed study was carried out to investigate the effects of poling on structure, vibrational, dielectric, and ferroelectric properties of donor-doped (V5+ at Ti4+-site) lead-free Na0.47Bi0.47Ba0.06Ti(1-x)VxO3, (xu2009=u20090, 0.01, and 0.03) ceramics fabricated via a modified sol-gel method. Rietveld refinement of synchrotron radiation source powder x-ray diffraction data showed that unpoled samples are in rhombohedral R3c phase whereas poled samples showed a mix rhombohedral R3c and tetragonal P4mm phases at ambient temperature, due to a long-range order established in lattice system after poling. V+5 doping increases the rhombohedral distortion in unpoled and poled samples while it reduces the tetragonality in poled samples. Vibrational study revealed that unpoled samples have more lattice disorder compared to poled samples. X-ray absorption near edge spectroscopy measurement confirmed that Ti and V are in 4+ and 5+ oxidation states, respectively, for all poled and unpoled samples. The average grain size was found to decrease from 5.6u2009±u20090.5u2009μm for xu2009=u20090 to 1.0u2009±u20090.2u2009μm for xu2009=u20090.03. Depolarization temperature was found to increase significantly in poled samples from ∼104u2009°C for undoped sample to 150u2009°C for the sample with 1% vanadium substitution. Drastic improvements in ferroelectric and dielectric properties are explained in terms of structural changes. High remnant polarization Pru2009∼u200931.4 μC/cm2 and moderately low coercive field Ec ∼ 20u2009kV/cm have been observed at an applied electric field of ∼35u2009kV/cm for the sample with 1% vanadium substitution which makes it an attractive candidate for ferroelectric applications.A detailed study was carried out to investigate the effects of poling on structure, vibrational, dielectric, and ferroelectric properties of donor-doped (V5+ at Ti4+-site) lead-free Na0.47Bi0.47Ba0.06Ti(1-x)VxO3, (xu2009=u20090, 0.01, and 0.03) ceramics fabricated via a modified sol-gel method. Rietveld refinement of synchrotron radiation source powder x-ray diffraction data showed that unpoled samples are in rhombohedral R3c phase whereas poled samples showed a mix rhombohedral R3c and tetragonal P4mm phases at ambient temperature, due to a long-range order established in lattice system after poling. V+5 doping increases the rhombohedral distortion in unpoled and poled samples while it reduces the tetragonality in poled samples. Vibrational study revealed that unpoled samples have more lattice disorder compared to poled samples. X-ray absorption near edge spectroscopy measurement confirmed that Ti and V are in 4+ and 5+ oxidation states, respectively, for all poled and unpoled samples. The average grain size was...

Lithium ion conduction in sol-gel synthesized LiZr2(PO4)3 polymorphs

Safety issue associated with the high flammability and volatility of organic electrolytes used in commercial rechargeable lithium ion batteries has led to significant attention to ceramic-based solid electrolytes. In the present study, lithium ion conduction in two polymorphs of LiZr2(PO4)3 synthesized via the sol-gel route has been investigated. Rietveld refinement of room temperature X-ray diffraction data of LiZr2(PO4)3 powders calcined at 900 °C and 1300 °C confirmed these to be the monoclinic phase with P21/n structure and rhombohedral phase with R3c structure, respectively. Increase in calcination temperature and resultant phase transformation improved the room temperature conductivity from 2.27×10−6 ohm-1m−1 for the monoclinic phase to 1.41×10−4 ohm−1m−1 for rhombohedral phase. Temperature dependence of conductivity was modeled using Arrhenius law and activation energy of ∼ 0.59 eV (for monoclinic phase) and ∼0.50 eV (for rhombohedral phase) were obtained.Safety issue associated with the high flammability and volatility of organic electrolytes used in commercial rechargeable lithium ion batteries has led to significant attention to ceramic-based solid electrolytes. In the present study, lithium ion conduction in two polymorphs of LiZr2(PO4)3 synthesized via the sol-gel route has been investigated. Rietveld refinement of room temperature X-ray diffraction data of LiZr2(PO4)3 powders calcined at 900 °C and 1300 °C confirmed these to be the monoclinic phase with P21/n structure and rhombohedral phase with R3c structure, respectively. Increase in calcination temperature and resultant phase transformation improved the room temperature conductivity from 2.27×10−6 ohm-1m−1 for the monoclinic phase to 1.41×10−4 ohm−1m−1 for rhombohedral phase. Temperature dependence of conductivity was modeled using Arrhenius law and activation energy of ∼ 0.59 eV (for monoclinic phase) and ∼0.50 eV (for rhombohedral phase) were obtained.

Synthesis and electrical properties of Li[Ni1/3Mn1/3Co1/3]O2

Among cathode materials for Li-ion batteries, layered Li[Ni,Co,Mn]O2 with hexagonal structure have drawn significant attention recently due to their excellent energy density. In the present study, Li[Ni1/3Mn1/3Co1/3]O2 was prepared using a sol-gel assisted combustion method. Rietveld refinement of room temperature X-ray diffraction data confirmed the crystallization of single-phase hexagonal Li[Ni1/3Mn1/3Co1/3]O2 in space group R3¯m with calculated lattice parameters a = 2.8615(8) A and c = 14.229(1) A. Impedance spectroscopy was used to study the electrical properties of LMN ceramics. DC conductivity was found to be 5.1×10−3 Ω−1m−1 at room temperature and obeyed the Arrhenius relation with activation energy EA = 0.27±0.01 eV.