Structure,dielectric and optical properties of Bi1.5+xZnNb1.5O7+1.5x pyrochlores

Non-stoichiometric pyrochlore ceramics with formula Bi_1.5+xZnNb_1.5O_7+1.5x were systematically investigated. Crystal structures of the compounds were studied by X-ray diffraction (XRD) technique. The structures were identified as pure cubic pyrochlores when |x| < 0.1. Dielectric and optical properties of the compositions when x = −0.1, 0 and 0.1 were studied. All samples have high resistivities and low dielectric loss. With increasing x in Bi_1.5+xZnNb_1.5O_7+1.5x, the lattice constant, permittivity, temperature coefficient of permittivity and thermal expansion coefficient increased, while dielectric loss decreased. Raman spectra indicated that the intensity of Bi–O stretching become stronger with increasing x. A vibration mode emerging at 861 cm⁻¹ when x = −0.1 means that the B–O coordination environment is significantly more disordered. Absorption spectra suggested that the bandgap energy become lower from 2.86 to 2.70 eV as lattice constants increased. Strong absorption occurs at wavelengths from 433 to 459 nm, shows that samples have the ability to respond to wavelengths in the visible light region.     

Structural,magnetic, vibrational and impedance properties of Pr and Ti codoped BiFeO3 multiferroic ceramics

Single-phase (Bi_1−xPr_x)(Fe_1−xTi_x)O₃ ceramics (x=0.03, 0.06, and 0.10 as BPFT-3, BPFT-6 and BPFT-10, respectively) were synthesized by conventional solid state reaction method. The effect of varying Pr and Ti codoping concentration on the structural, magnetic, dielectric and optical properties of the BPFT ceramics have been investigated. X-ray diffraction indicated pure rhombohedral phase formation for BPFT-3 and BPFT-6 ceramics, however, a structural phase transition from a rhombohedral to an orthorhombic phase has been observed for BPFT-10 ceramic. The maximum remnant magnetization of 0.1824 emu/g has been observed in BPFT-6. With increasing codoping concentration the room temperature dielectric measurements showed enhancement in dielectric properties with reduced dielectric loss. UV–vis diffuse reflectance spectra demonstrated the strong absorption of light in the visible region for a band gap variation 2.31–2.34 eV. Infrared spectroscopy indicated the shifting of Bi/Pr–O and Fe/Ti–O bonds vibrations and change in Fe/Ti–O bond lengths. Decrease in the conductivity on increasing Pr and Ti concentration in BFO is attributed to an enhancement in the barrier properties leading to suppression of lattice conduction path arising due to lattice distortion as confirmed from impedance analysis.     

Structural,magnetic and optical properties of Ce substituted BiFeO3 nanoparticles

Ce substituted Bi_1−xCe_xFeO₃ (x=0.03, 0.05, 0.07 and 0.10) nanoparticles were prepared by a tartaric acid based sol–gel route. X-ray diffraction patterns and Raman spectra revealed a structural phase transition from rhombohedral to orthorhombic phase for x=0.10 sample. Room temperature magnetic measurements showed weak ferromagnetic ordering and enhancement in magnetization with increasing Ce concentration. The improved magnetic properties due to the breaking of spin cycloid with Ce substitution have been observed from electron spin resonance (ESR) study. The measured g-values for all samples are greater than 2 and the ESR lines shift towards higher g-value with increasing Ce concentration, indicating ferromagnetic nature of these samples. UV–visible diffuse reflectance spectra showed a sharp absorption in the visible region with two d–d and three charge transfer (C-T) transitions. Prominent red shift in the band gap indicates a significant change in the band structure of the doped nanoparticles.     

Optical and electrical properties of p-type Ag-doped ZnO nanostructures

Zn_1−xAg_xO nanoparticles (NPs) (x=0, 0.02, 0.04, and 0.06) were synthesized by a sol–gel method. The synthesized undoped ZnO and Zn_1−xAg_xO-NPs were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and UV–visible spectroscopy. The XRD patterns indicated that undoped and Ag-doped ZnO crystallize in a hexagonal wurtzite structure. The TEM images showed ZnO NPs with nearly spherical shapes, with particle size distributed over the nanometer range. Evidence of dopant incorporation is demonstrated in the XPS measurements of the Ag-doped ZnO NPs. The Raman measurements indicated that the undoped and Ag-doped ZnO-NPs had a high crystalline quality. From the result of UV–vis, the band-gap values of prepared undoped and Ag-doped ZnO were found to decrease with an increase in Ag concentration. The obtained undoped and Ag-doped ZnO nanoparticles were used as a source material to grow undoped and Ag-doped ZnO nanowires on n-type Si substrates, using a thermal evaporation set-up. Two probe method results indicated that the Ag-doped ZnO nanowires exhibit p-type properties.     

Structural,magnetic and dielectric behavior of Mg1−xCaxNiyFe2−yO4 nano-ferrites synthesized by the micro-emulsion method

Ca–Ni co-substituted samples of nanocrystalline spinel ferrites with chemical formula Mg_1−xCa_xNi_yFe_2−y O₄ (x=0.0–0.6, y=0.0–1.2) were synthesized by the micro-emulsion method and were annealed at 700 °C for 7 h. The synthesized samples were characterized by x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, vibrating sample magnetometry (VSM) and dielectric measurements. The XRD and FTIR analysis reveals that single phase samples can be achieved by substituting Ca and Ni ions at Mg and Fe sites respectively in cubic spinel nano-ferrites. The crystallite size of the synthesized samples was found in the range 29–45 nm. The saturation magnetization (M_s) increases from 9.84 to 24.99 emu/g up to x=0.2, y=0.4 and then decreases, while the coercivity (H_c) increases continuously from 94 to 153 Oe with the increase in dopants concentration. The dielectric properties of these nano materials were also studied at room temperature in the frequency range 100 MHz to 3 GHz. The dielectric parameters were found to decrease with the increased Ca–Ni concentration. Further the peaking behavior was observed beyond 1.5 GHz. The frequency dependent dielectric properties of all the samples have been explained qualitatively on the basis of the Maxwell–Wagner two-layer model according to Koop's phenomenological theory. The enhanced magnetic parameters and reduced dielectric properties make the synthesized materials suitable for switching and high frequency applications, respectively.     

Effect of Dy-substitution on structural,electrical and magnetic properties of multiferroic BiFeO3 ceramics

The polycrystalline samples of dysprosium (Dy)-modified bismuth ferrite (i.e., Bi_1−xDy_xFeO₃; x=0–0.2 with the interval of 0.05) (BDFO) were synthesized using a high-temperature solid-state reaction method. Preliminary X-ray structural analysis showed that the reported crystal structure of BiFeO₃ (rhombohedral) is invariant even with Dy-substitution at the Bi-site upto x=0.2. The scanning electron micrograph of the compounds showed (i) the uniform distribution of grains on the sample surface with high density and (ii) reduction of grain size on increasing Dy content in BiFeO₃ (BFO). Studies of impedance, electrical modulus and electric conductivity of the materials in wide frequency (10–1000 kHz) and temperature (30–500 °C) ranges using a complex impedance spectroscopy technique have provided new and interesting information on the contribution of grains, grain boundary and interface in these parameters. Detailed studies of impedance spectroscopy clearly exhibit the dielectric relaxation of non-Debye type. The ac conductivity of the Dy-substituted BFO obeyed Jonscher's universal power law. An increase in Dy-content in BDFO results in the increase of spontaneous magnetization of BFO due to the collapse of spin cycloid structure.     

Structural,dielectric, vibrational and magnetic properties of Sm doped BiFeO3 multiferroic ceramics prepared by a rapid liquid phase sintering method

Rare earth Sm substituted Bi_1−xSm_xFeO₃ with x=0, 0.025, 0.05, 0.075 and 0.10 polycrystalline ceramics were synthesized by a rapid liquid phase sintering method. The effect of varying composition of Sm substitution on the structural, dielectric, vibrational, optical and magnetic properties of doped BiFeO₃ (BFO) ceramics have been investigated. X-ray diffraction patterns of the synthesized rare earth substituted multiferroic ceramics showed the pure phase formation with distorted rhombohedral structure with space group R3c. Good agreement between the observed and calculated diffraction patterns of Sm doped BFO ceramics in Rietveld refinement analysis of the X-ray diffraction patterns and Raman spectroscopy also confirmed the distorted rhombohedral perovskite structure with R3c symmetry. Dielectric measurements showed improved dielectric properties and magnetoelectric coupling around Néel temperature in all the doped samples. FTIR analysis establishes O–Fe–O and Fe–O stretching vibrations in BiFeO₃ and Sm-doped BiFeO₃. Photoluminescence (PL) spectra showed visible range emissions in modified BiFeO₃ ceramics. The magnetic hysteresis measurements at room temperature and 5 K showed the increase in the magnetization with the increase in doping concentration of Sm which is due to the structural distortion and partial destruction of spin cycloid caused by Sm doping in BFO ceramics.     

Structural and dielectric properties of Bi1−xSrxMnO3 (0.40≤x≤0.55)

In order to study the effect of Sr substitution on structural and dielectric properties of Bi_1−xSr_xMnO₃ (0.40≤x≤0.55) compounds were synthesized by the solid state reaction method. The as-prepared samples were characterized by X- ray diffraction (XRD) and dielectric measurements to correlate structural changes with dielectric properties. The XRD data were further analyzed by the Rietveld refinement. The highest dielectric constant was observed in Bi_0.55Sr_0.45MnO₃ and Bi_0.5Sr_0.5MnO₃ systems (∼10⁶) mainly because of orientation polarization. The charge ordering temperature decreases with increasing Sr concentration in Bi_1−xSr_xMnO₃ systems.     

Raman scattering, electronic structure and microwave dielectric properties of Ba([Mg1−xZnx]1/3Ta2/3)O3 ceramics

Effects of Zn substitution for Mg on the crystal structure, lattice vibrations and microwave dielectric properties of Ba(Mg_1/3,Ta_2/3)O₃ (BMT) ceramics were investigated. Raman scattering spectra for Ba([Mg_1−xZn_x]_1/3Ta_2/3)O₃ (BMZT) ceramics, with x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0, were measured at room temperature. The Raman result shows a dominance of 1:2 ordered structure at all Zn substitution contents. All Raman modes shift to lower frequencies with increasing Zn substitution. Higher Qf value correlates well with narrower width of the breathing Raman mode A_1g(4) and larger relative intensity of 1:2 long-range-ordered mode E_g(2) in BMZT solid solution. First-principle calculation was performed to investigate the electronic structure of 1:2 ordered BMT and Ba(Zn_1/3,Ta_2/3)O₃ (BZT). Covalent bond between Zn and O in BZT is much stronger than that between Mg and O in BMT due to the Zn 3d orbital. Zn substitution for Mg leads to longer and weaker Ta-O bonds, which may be one reason for the variation of Raman spectroscopy and microwave dielectric properties of BMZT system.     

Synthesis,structural analysis and dielectric properties of Ba8(Mg1−xZnx)Nb6O24 hexagonal perovskites

Ba₈(Mg_1−xZn_x)Nb₆O₂₄ (x=0, 0.2, 0.4, 0.6, 0.8 and 1) ceramics were prepared through the conventional solid-state route. The materials were calcined at 1250 °C and sintered at 1375–1425 °C. The structure of the system was analyzed using X-ray diffraction and vibrational spectroscopic studies. The microstructure of the sintered pellet was analyzed using scanning electron microscopy. The dielectric constant (ε_r), temperature coefficient of resonant frequency (τ_f) and the unloaded quality factor (Q_u) were measured in the microwave frequency region. The τ_f values of the compositions were reduced by varying the value of x from 0 to 1. The dielectric responses to frequency were also studied in the radio frequency region. The compositions have good microwave dielectric properties and hence are suitable for dielectric resonator applications.     

A-site strontium doping effects on structure,magnetic, and photovoltaic properties of (Bi1−xSrx)FeO3−δ multiferroic ceramics

Raman spectroscopy, X-ray diffraction (XRD), magnetization hysteresis loop, synchrotron X-ray absorption spectroscopy, and photovoltaic effects have been measured in (Bi_1−xSr_x)FeO_3−δ (BFO100xSr) ceramics for x=0.0, 0.05, 0.10, and 0.15. Raman spectra and XRD reveal a rhombohedral R3c structure in all compounds. A-site Sr²⁺ doping increases fluctuations in cation-site occupancy and causes broadening in Raman modes. BFO15Sr exhibits a strong ferromagnetic feature due to reduction of FeOFe bond angle evidenced by the extended synchrotron X-ray absorption fine structure. The heterostructure of indium tin oxide (ITO) film/(Bi_1−xSr_x)FeO_3−δ ceramic/Au film exhibit clear photovoltaic (PV) responses under blue illumination of λ=405 nm. The maximal power-conversion efficiency and external quantum efficiency in ITO/BFO5Sr/Au are about 0.004% and 0.2%, respectively. A model based on optically excited charges in the depletion region between ITO and (Bi_1−xSr_x)FeO_3−δ can well describe open-circuit voltage and short-circuit current as a function of illumination intensity.     

Piezoelectric and dielectric properties of (Bi0.5Na0.5)0.94Ba0.06TiO3–Ba(Zr0.04Ti0.96)O3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of (1 − x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–xBa(Zr_0.04Ti_0.96)O₃ (abbreviated as BNBT–BZT100x, wherein x from 0 to 10 mol%) were fabricated. We have studied effects of amount of BZT content on the electrical properties and microstructures. X-ray diffraction analysis indicates that a solid solution is formed when BZT diffuses into the BNBT lattice, and further the crystal structure of sintered hybrid changes from rhombohedral to tetragonal symmetry along with increasing BZT content. Piezoelectric property measurements reveal that the BNBT–BZT4 ceramics has the highest piezoelectric performance, for example, the piezoelectric constant d₃₃ reaches to 167 pC/N and planar electromechanical coupling factor k_p is up to 0.27. In addition, the effect of Bi₂O₃ on the electrical properties and microstructure of the BNBT–BZT4 ceramics have also been studied, and found that the doping of Bi enhances the piezoelectric properties of ceramics.     

Dispersion studies of La substitution on dielectric and ferroelectric properties of multiferroic BiFeO3 ceramic

Lanthanum La-substituted multiferroic Bi_1−xLa_xFeO₃ ceramics with x = 0.0, 0.05, 0.10, 0.15, 0.20 and 0.25 have been prepared by solution combustion method. The effect of La substitution for the dispersion studies on dielectric and ferroelectric properties of Bi_1−xLa_xFeO₃ samples have been studied by performing x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), density, dc resistivity and dielectric measurements as well as characterizing the polarization-field hysteresis loop. The results of prepared samples are compared with those of bismuth ferrite (BiFeO₃). In the measuring frequency of 10 KHz to 1 MHz, the dielectric constants and dielectric losses for samples x = 0.20, 0.25 are almost stable and exhibited lowest dielectric loss close to 0.1. The resistivity of Bi_1−xLa_xFeO₃ samples reaches a maximum value of 10⁹ ohm-cm, which is about three times higher than that for pure BiFeO₃. The results also show that stabilization of crystal structure and nonuniformity in spin cycloid structure by La substitution enhances the resistivity, dielectric and ferroelectric properties. Furthermore, the substitution of rare earth La for Bi helps to eliminate the impurity phase in BiFeO₃ ceramic.     

Dielectric properties of Bi-doped Ba0.8Sr0.2TiO3 ceramic solid solutions

Bismuth-doped barium–strontium–titanate ceramics of the formula (Ba_0.8Sr_0.2)_(1−1.5y)Bi_yTiO₃ were prepared using a conventional solid-state reaction method. The structure, dielectric properties, and ferroelectric relaxor behaviour of all compositions were thoroughly investigated. The findings revealed a broad dielectric anomaly and a shift in dielectric maxima towards higher temperatures with increasing frequency. The diffuseness degree indicator γ was about 1.68, and dielectric relaxation was noted to follow the Vogel–Fulcher relationship, with T_f=185 K, f₀=1.18×10¹⁰ Hz, and Ea=0.35 eV, which further supported the spin-glass-like properties of BBSTs. The latter were also noted to display significant ferroelectric relaxor behaviour that could be attributed to the presence of Bi³⁺ doping ions. The degree of relaxation behaviour was noted to increase with the increase in bismuth concentration. Raman spectra were investigated as a function of temperature, and the findings confirmed the results from X-ray and dielectric measurements. Among the compositions assayed in this solid solution, 10% Bi-doped Ba_0.8Sr_0.2TiO₃ yielded promising relaxor properties that make it a strong candidate for future industrial application in the production of efficient and eco-friendly relaxor ferroelectric materials.     

Structural,magnetic and photocatalytic properties of Sr-doped BiFeO3 nanoparticles based on an ultrasonic irradiation assisted self-combustion method

A novel ultrasonic irradiation assisted self-combustion method was developed to prepare single-phase Bi_1−xSr_xFeO_3−δ (BSFO) nanoparticles, which were charactered by XRD, SEM, TEM and UV–vis spectra. The results show that structure, as well as magnetic and photocatalytic properties of BSFO are influenced by the particle size and the Sr²⁺ dopant content. Regarding smaller particles, even if small amount of Sr²⁺ substitution content change can result in the phase transition from the rhombohedral distorted perovskite to the cubic. The doping of heterovalent Sr²⁺ ions in BiFeO₃ (BFO) nanoparticles improves the ferromagnetic property. As ultrasonication can generate particles with larger surface area and more defections, BSFO nanoparticles exhibit efficient photocatalytic activity as a promising photocatalyst.     

Physical properties of new,lead free (Na0.5Bi0.5)(1−x)BaxTi(1−x)(Fe0.5Nb0.5)xO3 ceramics

This study reports on the synthesis of polycrystalline samples of (Na_0.5Bi_0.5)_(1−x)Ba_xTi_(1−x)(Fe_0.5Nb_0.5)_xO₃ with x=0, 0.025, 0.05, 0.075, and 0.1, using the solid-state reaction technique. It investigates the effects of the substitution of sodium and bismuth by barium in the A site and of titanium by iron and niobium in the B site with regard to the free NBT symmetry and dielectric properties were investigated. The crystallographic and dielectric properties were also investigated. The diffractograms showed that all the samples had a single phase character. The increase of ceramic lattice parameters induced an increase in the size of the perovskite lattice. This increase was caused by the increase of the radii of the A and B sites. Room temperature X-ray data revealed that the ceramic structures underwent a gradual distortion with the increase in the composition fraction. Dielectric permittivity was measured in the temperature range of 120–780 K with frequencies ranging from 1 to 10³ KHz. Three anomalies, namely T_d, T₁ and T_m, were detected and noted to coexist at lower T_d and T_m as the rate of substitutions increased. All the samples exhibited a diffuse phase transition and implied better dielectric permittivity maxima values at temperatures approaching room temperature, since the substitution rate values increased more than that of pure NBT. A relaxor behavior with ΔT_m=14 K and ε'_rmax=3876 at 1 kHz was observed for (Na_0.5Bi_0.5)_0.9Ba_0.1Ti_0.9(Fe_0.5Nb_0.5)_0.1O₃ ceramic.     

Microstructures,magnetic, and dielectric properties of Ba-doped BiFeO3 nanoparticles synthesized via molten salt route

As the paradigm of magnetoelectric multiferroic materials, BiFeO₃ (BFO) has potential applications in spintronics, memory devices, sensors, and actuators. However, its large leakage current and small magnetism at room temperature restrict its practical applications. It is demonstrated that the substitutions of Bi by alkali earth elements at A-site of BFO can significantly reduce the leakage current and enhance the remanent magnetization of BFO. In this work, Ba-doped BFO nanoparticles Bi_1-xBa_xFeO₃ (x = 0, 0.05, 0.10, 0.15 and 0.20) were synthesized via molten salt route. X-ray diffraction patterns revealed that with increasing the Ba-doped content the formation of the impurity phase was depressed and the rhombohedral distortions of these nanoparticles were suppressed, as confirmed by Raman spectra. X-ray photoelectron spectroscopy measurements reveal that the Fe element in the nanoparticles exists in the dual valence states of Fe³⁺ and Fe²⁺, and two kinds of oxygen atoms (lattice oxygen atoms and the adsorbed oxygen atoms) exist in the nanoparticles. With increasing the Ba-doped content, the content ratios of Fe³⁺ to Fe²⁺ ions were generally increased, whereas the oxygen vacancy concentrations were decreased. The average particle sizes of the Ba-doped BFO nanoparticles were decreased as compared with that of nondoped BFO nanoparticles. In contrast, the room temperature magnetization of the Ba-doped BFO nanoparticles was greatly enhanced by Ba-substitution, as confirmed by the M-H loops. At room temperature, the remanent magnetization and coercive field of the Bi_0.8Ba_0.2FeO₃ nanoparticles were 0.51 emu/g and 1130 Oe, respectively. Furthermore, the leakage current density was reduced by one order of magnitude at x = 0.2 and the dielectric properties are also improved by Ba-substitution. The improvements on the remanent magnetization, leakage current density as well as dielectric properties of the Ba-doped BFO nanoparticles make them promising candidates for spintronics and dielectric energy storages.     

High energy-storage properties of [(Bi1/2Na1/2)0.94 Ba0.06] La(1−x) ZrxTiO3 lead-free anti-ferroelectric ceramics

Energy-storage properties of [(Bi_1/2Na_1/2)_0.94Ba_0.06]La_(1−x)Zr_xTiO₃ (BNT-BLZT, x=0, 0.02, 0.04, and 0.06) lead-free anti-ferroelectric ceramics fabricated via the conventional sintering technique were first investigated. Calculation from the X-ray diffraction results reveals that BNT-BLZT ceramic possesses a single perovskite structure phase. In addition, the P–E hysteresis loops measured at room temperature show that the BNT-BLZT (x=0.02) ceramics obtain the maximum P value of 37.5 μC/cm² and the largest energy-storage density W_max is 1.58 J/cm³. The temperature dependence of dielectric permittivity ε_r and dielectric loss tanδ illustrate that the addition of Zr can improve the piezoelectric properties of BT-BLZT ceramics. These properties indicate that BNT-BLZT ceramics might be a promising lead-free anti-ferroelectric material for energy storage application.     

Structural and magnetic properties of NiFe2−xBixO4 (x = 0, 0.1, 0.15) nanoparticles prepared via sol-gel method

NiFe_2−xBi_xO₄ (x = 0, 0.1, 0.15) nanopowders were synthesized via sol-gel method. The precursor gels were calcined at 773 K in air for 1 h to obtain the pure nanostructured NiFe_2−xBi_xO₄ spinel phase. The crystal structure and magnetic properties of the substituted spinel series of NiFe_2−xBi_xO₄ have been investigated by means of ⁵⁷Fe Mössbauer spectroscopy, transmission electron microscopy and alternating gradient force magnetometry. Mössbauer spectroscopic measurements revealed that Bi³⁺ cations tend to occupy octahedral positions in the structure of the substituted ferrite, i.e., the crystal-chemical formula of the as-prepared nanoparticles may be written as: (Fe)[NiFe_1−xBi_x]O₄ (x = 0, 0.1, 0.15), where parentheses and square brackets enclose cations on sites of tetrahedral and octahedral coordination, respectively. Selective area electron diffraction studies provided evidence that the samples of the NiFe_2−xBi_xO₄ series, independently of x, exhibit the cubic spinel structure. The values of the saturation magnetization and the coercive field of NiFe_2−xBi_xO₄ nanoparticles were found to decrease with increasing degree of bismuth substitution.     

Microstructural and electrical behavior of Bi4V2−xCuxO11−δ (0 ≤ x ≤ 0.4)

Cation substituted bismuth vanadate possesses high oxygen ion conductivity at lower temperatures. The ionic conductivity of this material at 300 °C is 50–100 times more than any other solid electrolyte. Three phases (α, β, γ) are observed in the substituted compound; α and γ are low and high conducting phase, respectively. Samples of Bi₄V_2−xCu_xO_11−δ (x = 0–0.4) were prepared by solid-state reaction technique. Impedance spectroscopy measurements were carried out in the frequency range of 100 Hz to 100 kHz using gold sputtered cylindrical shaped pellets to obtain bulk ionic conductivities as a function of the substitution and temperature. The change of slopes observed in the Arrhenius plots is in agreement with the phase transitions for all the compositions. The highest ionic conductivity of the Cu-substituted compound was observed in Bi₄V_1.8Cu_0.2O_11−δ which is attributed to its lower activation energy. Microstructural studies indicated the stabilization of high temperature γ-phase at low temperature in those samples whose ionic conductivity observed was higher.