The crossover of (Ba<Subscript>1−x</Subscript>Ca<Subscript>x</Subscript>)(Ti<Subscript>0.9</Subscript>Sn<Subscript>0.1</Subscript>)O<Subscript>3</Subscript> piezoelectric ceramics from single-phase to composite with studying the structural and dielectric properties

Lead-free (Ba_1?xCa_x)(Ti_0.9Sn_0.1)O₃ perovskite ceramics (x?=?0.02–0.5) (BCTS) were synthesized using the solid-state reaction technique. X-ray diffraction was used to identify the formed phases of the prepared compositions. The morphology of ceramics has been studied using a scanning electron microscope equipped with an energy dispersive spectrometer. Field emission scanning electron microscope was used to examine the morphology of sensing film calcined powder. The crossover from BCTS single-phase (x?=?0.02) to BCTS composite(x?=?0.5) was obtained via coexistence of both (x?=?0.3) of Ca addition. The composite powder was sintered at higher temperature rather than the single-phase powder. The calcined powder sensing film was prepared by the screen-printing technique as humidity sensors. Thereafter, DC resistance measurements were performed in the presence of relative humidity RH at room temperature. All the compositions exhibited a poor sensitivity toward the humidity sensing in the range of 0–98% RH. The compositions 0.02 and 0.06 have shown orthorhombic–tetragonal phase transition (T_O?T) below the room temperature, while the other compositions have shown a pure tetragonal phase. The highest value of permittivity at Curie temperature (ε?=?29241 at 100 Hz) and piezoelectric coefficient (d₃₃?=?495 pC/N) at room temperature were obtained at Ca?=?0.06 due to present polymorphic phase transition. The effect of frequency on the dielectric constant and dielectric loss at room temperature were investigated. All the prepared compositions exhibited small values of dielectric loss from 50 Hz up to 100 KHz, which indicates a good reliability for electronic applications such as capacitors or memory devices.     

Influence of samarium doping on structural and dielectric properties of strontium bismuth tantalate ceramics derived by molten salt synthesis route

Layered Sr(Bi_1?xSm_x)₂Ta₂O₉ ceramics with x ranging from 0 to 0.10 (10 mol%) were fabricated by the low temperature molten salt synthesis route. X-ray powder diffraction studies revealed that the single phase orthorhombic layered perovskite structure is retained in all these compositions. Scanning electron microscopic studies on these ceramics confirmed the presence of well packed equiaxed plate shaped grains. The dielectric and electrical conductivity properties were studied in the 100 Hz–1 MHz frequency range at 300 K. Interestingly, the 10 mol% samarium doped SrBi₂Ta₂O₉ ceramics exhibited high dielectric constant (ε_r = 155) and low dielectric loss (0.00298) compared to those of other compositions. The electrical conductivity of undoped and samarium doped ceramics increased linearly with increase in frequency.     

Preparation,characterization and dielectric properties of Ba3−xSrxM4Ti4O21 (M = Nb,Ta and 0 ≤ x ≤ 3) ceramics

Ba_3−xSr_xM₄Ti₄O₂₁ (M = Nb, Ta and 0 ≤ x ≤ 3) ceramics have been prepared through solid state ceramic route. The structure and microstructure of the compositions have been studied using powder X-ray diffraction and Scanning Electron Microscopic studies. In the present study, both Ba₃Nb₄Ti₄O₂₁ and Ba₃Ta₄Ti₄O₂₁ are obtained as single phase compositions whereas strontium rich compositions exhibit multiphase in nature. Energy dispersive X-ray analysis has been performed to identify the nature of additional phases present in the strontium rich compositions. The dielectric constant, dielectric loss and temperature variation of dielectric constant of the well sintered ceramic specimens have been studied in the low frequency region (< 13 MHz) using an impedance analyzer. The present study reveals that high dielectric compositions can be realized by Sr-substitution in the BaO–TiO₂–Nb₂O₅/Ta₂O₅ ternary systems.     

Structural, optical and photoluminescence studies of heavily Mn-doped ZnO nanoparticles annealed under Ar atmosphere

Undoped and heavily Mn-doped with ZnO nanoparticles (Zn_1?xMn_xO, x?=?0.0, 0.05, 0.1 and 0.2) annealed under Ar atmosphere have been synthesized by a sol–gel method. The structural properties and optical absorption of the prepared samples have been examined by powder X-ray diffraction, energy dispersive X-ray analysis, Fourier transform infrared (FTIR) spectroscopy and UV–visible spectrophotometer. Hexagonal wurtzite structure of the samples is confirmed by the XRD spectra. The average crystalline size of the Zn_1?xMn_xO nanoparticles has been calculated from X-ray line broadening and is decreased from 35.73 to 18.24?nm with increase in Mn concentrations from 0.0 to 0.2. The increase in lattice parameters indicates the substitution of Mn in ZnO lattice. SEM and TEM photographs indicated that the grain size of undoped ZnO is bigger than the Mn-doped ZnO which is due to the limitations of grain growth upon Mn doping. The presence of functional groups and the chemical bonding due to Mn doping is confirmed by FTIR spectra. PL spectra of the Zn_1?xMn_xO system showed that the shift in near band edge emission at 390?nm and a blue band emission at 450–490?nm which confirms the substitution of Mn.     

Influence of cerium substitution on structural,magnetic and dielectric properties of nanocrystalline Ni–Zn ferrites synthesized by combustion method

Nickel–Zinc (Ni–Zn) ferrites substituted by cerium (Ce) and having the chemical composition Ni_0.5Zn_0.5Ce _x Fe_2?x O₄ (x?=?0.00, 0.02, 0.04, 0.06, 0.08 and 0.10) were synthesized by combustion method using the organic fuel urea as reducing agent. The effects of cerium substitution on the structural, magnetic and dielectric properties of Ni–Zn compounds have been evaluated. X-ray diffraction patterns indicate that the Ni_0.5Zn_0.5Ce _x Fe_2?x O₄ crystallizes into cubic spinel structure initially and secondary phase emerged along with main spinel phase when the Ce³⁺ content is increased. The elemental composition analysis confirms the stoichiometric presence of expected elements in the samples. Scanning electron microscope and high-resolution transmission electron microscope images reveal the nature of grain growth and the particle size of the synthesized samples. Fourier transform infrared spectroscopy confirms the formation of spinel phase and predicted the shifting of bands corresponding to Fe–O vibrations towards higher wavenumbers compared to undoped Ni–Zn ferrite. Magnetic characterization studies reveal that the substitution of Ce³⁺ into the Ni–Zn ferrite leads to a significant change in saturation magnetization and coercivity values. A plot of dielectric constant (?′) versus applied electrical frequency measured at room temperature shows the normal dielectric behavior of the spinel ferrites. The introduction of Ce³⁺ rare earth ions into Ni–Zn ferrites samples is found to affect the values of both dielectric constant and AC conductivity.     

Structural and high temperature conduction studies of (Na<Subscript>0.46</Subscript>Bi<Subscript>0.46</Subscript>Ba<Subscript>0.08</Subscript>) (Mn<Subscript>x</Subscript>Ti<Subscript>1−x</Subscript>O<Subscript>3</Subscript>)–CuO lead-free piezoelectric ceramics

Polycrystalline lead-free (Na_0.46Bi_0.46Ba_0.08)(Mn_xTi_1?xO₃)?+?0.2CuO ceramics (x?=?0.0, 0.5, 2.0, 3.0 wt%) were prepared via solid-state reaction method. X-ray diffraction (XRD) analysis confirmed the formation of single-phase perovskite structure and indicated the presence of morphotropic phase boundary, where the tetragonal and rhombohedral phases co-existed for all the synthesized compositions. Scanning electron microscopy (SEM) analysis revealed that the average grain size decreased with the increase in Mn content. Impedance spectroscopy (IS) indicated that Mn doping was found to decrease the grain boundary resistance. Two semi-circles were observed for higher Mn content which indicates the contribution of both bulk grains and grain boundaries. Non-Debye type and temperature dependent relaxation phenomenon was also revealed by IS studies. The activation energies at different frequencies were found to be 0.05–0.9 eV, indicating hopping charge conduction mechanism. These results have comprehensive implications for the expanded use of BNT based lead free piezoelectric ceramics for practical applications.     

Studies of structural and magnetic properties of sol–gel synthesized cobalt substituted Zn–Mn chromites

Cobalt substituted Zn–Mn chromites Zn_1?xCo_xMnCrO₄ (0 ≤ x ≤ 1) were prepared by sol–gel method. The synthesized material was characterized by various physico-chemical methods. The temperature of decomposition, crystallization and phase transformation of the as-prepared powder was studied using TGA–DTA measurement. X-ray diffraction patterns revealed that all compositions are in single phase cubic structure. An infra-red spectral study shows two strong bands, which is attributed to the intrinsic vibrations of tetrahedral sites and the octahedral sites. Formation of spherical particles was revealed by scanning electron microscopy analysis. The elemental analysis as obtained from energy dispersive analysis of X-ray is in close agreement with the expected composition from the stoichiometry of reactant solutions used. Magnetic properties were measured by vibrating sample magnetometer. All the compositions indicated ferrimagnetic nature. The substitution of cobalt ions in the lattice affected the structural as well as magnetic properties of spinel.     

Investigation of the lithium-rich boundary of the Li1+x Mn2−x O4 cubic spinel phase in air

Several compositions of the cubic spinel Li_1+x Mn_2?x O_4?δ phase in the lithium–manganese–oxygen (Li–Mn–O) system were synthesized at 700, 750, and 800 °C in air ( $ p_{{{\text{O}}_{2} }} $  = 0.2 atm) to investigate the Li-rich boundary of the cubic spinel phase at these temperatures. The lattice parameters of the several compositions were determined by Rietveld analysis of the measured X-ray patterns, and the Li and Mn contents of the samples were measured using inductively coupled plasma with optical emission spectroscopy (ICP-OES). A Vegard-like dependence of the measured lattice parameter of the cubic spinel phase with Li to Mn ratio exists in the homogeneity range of the cubic spinel. This dependence could be used to derive the boundary of the single phase cubic spinel field in the Li–Mn–O system at 700 and 750 °C at $ p_{{{\text{O}}_{2} }} $  = 0.2 atm and to estimate the Li-rich boundary at 800 °C. The results of the present study are compared with two other experimental studies on the homogeneity range of the cubic spinel phase in an attempt to resolve the contradiction between these two studies.     

Structural, microstructural and dielectric studies of tin-doped barium niobate perovskite

Monophasic oxides of the type Ba(Nb_1-x Sn _x ) O₃ (0 ≤ x ≤ 1) have been synthesized by solid-state reaction method. All these compounds are found to have tetragonal structure except x = 1. The cell parameters and their variation with composition x have been determined. The X-ray density is found to increase gradually with increase of dopant concentration. Tolerance factor and volume of unit cell was found to be almost constant for all the compositions. Scanning electron microscopy showed the presence of grains of approximately 1 μm in size. Dielectric measurements in the frequency range 100 Hz to 1 MHz and in the temperature range from − 100°C to 500°C has been carried out to determine the dielectric parameters. A strong frequency dependence of both dielectric constant (ɛ′) and dielectric loss (D) is observed in the frequency range 100 Hz to 100 kHz. At low frequency, the piling up of mobile charge carriers at the grain boundary produces interfacial polarization giving rise to high dielectric constant. Dielectric loss showed a typical behaviour in the temperature and frequency range studied.     

High-temperature resistivity and thermoelectric properties of coupled substituted Ca3Co2O6

Abstract

Polycrystalline samples of Ca_3?xNa_xCo_2?xMn_xO₆ (x=0.0–0.5) have been prepared by the sol-gel cum combustion method using sucrose in order to investigate the effects of the coupled substitution of Na and Mn on Ca and Co sites on the transport properties of Ca₃Co₂O₆(Co326). The products were characterized by Fourier transform infrared spectroscopy, powder x-ray diffraction (XRD), thermogravimetry (TGA), differential thermal analysis and scanning electron microscopy. XRD patterns reveal the formation of single-phase products up to x=0.5. Coupled substitution increases the solubility of both Na and Mn on Ca and Co sites, respectively, in contrast to the limited solubility of Na and Mn (x=0.2) when separately substituted. TGA confirms the formation of the Ca₃Co₂O₆ phase at temperatures ～720 °C. The grain size of the parent and substituted products is in the range 150–250 nm. Electrical resistivity and Seebeck coefficient were measured in the temperature range 300–800 K. Resistivity shows semiconducting behavior for all the compositions, particularly in the low-temperature regime. The Seebeck coefficient increases with temperature throughout the measured temperature range for all compositions. The maximum Seebeck coefficient (200 μV K^?1) is observed for x=0.5 at 825 K, and this composition may be optimal for high-temperature thermoelectric applications.     

Improved dielectric properties in pyrochlore type oxides: Ca3Sm3?xBixTi7Nb2O26.5 (x = 1.0, 2.0 or 3.0) by Bi substitution

Improved dielectric properties are observed in pyrochlore type oxides, Ca₃Sm_3−x Bi_xTi₇Nb₂O_26.5 (x = 1.0, 2.0 or 3.0) by Bi substitution. The dielectric constant increased with increasing Bi concentration. The dielectric constant obtained for Ca₃Bi₃Ti₇Nb₂O_26.5 is 110, whereas, without Bi (Ca₃Sm₃Ti₇Nb₂O_26.5) it is 62 at 100 kHz. The Powder X-ray diffraction analysis reveals that cubic pyrochlore type phase is formed for all the compositions. The experimental results further show that the formation of Bi substituted compounds is complete at a lower temperature than the compounds without Bi. Microstructure studies reveal that the grains formed are acicular when Bi is present in large amounts compared to cuboid grains in samples having no Bi.     

Polymeric citrate precursor route to the synthesis of nano-sized barium lead titanates

Monophasic oxides of the formula, Ba_1−xPb_xTiO₃ (0≤x≤1.0) were obtained at temperatures close to 500 °C from polymeric precursors formed using citric acid and ethylene glycol. These oxides were found to be tetragonal for all values of x, the distortion increasing with Pb content. Differential scanning calorimetry (DSC) shows that the decomposition of the precursor to the oxides varies with composition and the decomposition temperature is highest (530 °C) for the x=0.5 composition. X-ray line broadening studies of 900 °C sintered samples show grain size of 50-54 nm in all compositions. TEM studies show agglomerated grains of the size, 40-60 nm. The dielectric constant (ε) decreases with lead-doping having a value 70 for PbTiO₃. The dielectric loss (D) for different compositions varied between 0.005 and 0.01 at 100 kHz. The dielectric constant and loss show excellent frequency stability.     

X-ray diffraction,Mössbauer spectrometry and thermal studies of the mechanically alloyed (Fe1−xMnx)2P powders

(Fe_1?xMn_x)₂P phosphide powders in the composition range 0.15?≤?x ≤ 0.75 have been mechanically alloyed and their structural, magnetic and thermal changes with composition have been investigated by means of X-ray diffraction, ⁵⁷Fe Mössbauer spectrometry, magnetization measurements and differential scanning calorimetry. The milling process induces changes in the crystal phase diagram of the (Fe_1?xMn_x)₂P system. The XRD results reveal the coexistence of a bcc Fe(Mn)-type, hexagonal (Fe₂P and Mn₂P-type), orthorhombic (MnP-type) and tetragonal Fe₃P-type structures for all compositions. The room temperature Mössbauer spectra confirm the formation of the Fe(Mn)-type, non-stoichiometric Fe₂P-type, FeP-type and Fe₃P-type structures. Saturation magnetization exhibits a comparable behavior to that of the average hyperfine magnetic field. The DSC scans show the existence of several endothermic and exothermic peaks in the temperature range (100–700)?°C related to different phase transitions. The endothermic peak at about 582–589?°C can be related to the ferromagnetic/paramagnetic transition temperature (Curie temperature, T_C) of the Fe(Mn)-type structure.     

Ferroelectric, dielectric and piezoelectric properties of Pb1?xCex(Zr0.60Ti0.40)O3, 0?≤?x?≤?0.08

The ferroelectric, dielectric and piezoelectric properties of compositions Pb_1−x Ce _x (Zr_0.60Ti_0.40)O₃, (x = 0.0, 0.01, 0.02, 0.04, 0.06 and 0.08) are studied. The above compositions are prepared from their constituent oxides, calcined at 900 °C for 4 h and various phases present are characterized by X-ray diffraction (XRD) technique. The above powders are uniaxially pressed into circular compacts, sintered at 1,250 °C for 2 h, electroded, poled at 2 kV/mm D.C. voltage and their electrical properties are measured. The XRD analysis shows the presence of rhombohedral phase up to 2 mol% ceria while tetragonal phase found at higher concentrations. It is observed that the ferroelectric, dielectric and piezoelectric properties increase with the addition of ceria with a maximum at 2 mol% and then decreases. The higher piezo properties associated with low ceria concentration are attributed to rhombohedral phase.     

Crystallite structure,microstructure, dielectric,and piezoelectric properties of (Pb1.06−xBax)(Nb0.94Ti0.06)2O6 piezoelectric ceramics prepared using calcined powders with different phases

In an attempt to obtain dense lead metaniobate-based ceramics with improved dielectric and piezoelectric properties, the (Pb_1.06−xBa_x)(Nb_0.94Ti_0.06)₂O₆ (x = 0, 0.04, 0.08, 0.12) piezoelectric ceramics were prepared separately from the two kinds of calcined powders, i.e., the powders with the rhombohedral phase and orthorhombic phase. For obtaining the calcined powders with the different phases, two different calcination temperatures of 900 °C and 1250 °C were chosen. The calcined powders were characterized using X-ray diffraction, scanning electron microscope, laser particle size analyzer and differential scanning calorimetry. Effects of the phase structures of the calcined powders on crystallite structure, microstructure, dielectric and piezoelectric properties of the ceramics were studied in detail. The lattice parameters and grain size of the ceramics are related to the phase structures of the calcined powders. The doping of Ba²⁺ has an influence on the dielectric and piezoelectric properties of the ceramics. The ceramics with x = 0.08 fabricated from the calcined powders with the orthorhombic phase demonstrate the optimum dielectric and piezoelectric properties.     

High temperature growth, charge distribution and magnetism in Co and Mn co-doped ZnO

Zn_1?2xCo_xMn_xO (x = 0.03 and 0.05) bulk samples were synthesised by a standard high temperature solid state reaction technique at 1,400 °C. Characterization techniques X-ray diffraction, Vibrating Sample Magnetometry and Scanning Electron Microscopy with Energy Dispersive Analysis of X-rays were used to investigate effect of transition metal element Co and Mn incorporated in the system using high temperature technique. The magnetic, structural, electron density distribution and bonding properties have been investigated for the samples prepared in this work. X-ray diffraction analysis of the synthesized samples showed a single phase ZnO wurtzite structure for x = 0.03 and very slight segregation of a spinel phase for x = 0.05. Magnetization measurements indicate no evidence of ferromagnetism in co-doped (Co and Mn) ZnO. The structural and electron density analysis presented in this work is based on the actual concentrations of Co and Mn ions introduced in the matrix which nearly coincide with the nominal concentrations.     

Effect of Gd-substitution on phase transition and conduction mechanism of BiFeO3

The polycrystalline sample of (Bi_0.8Gd_0.2)FeO₃ was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray structural analysis of the sample confirms the formation of the desired compound with rhombohedral phase. The scanning electron micrograph of the sample showed uniform distribution of the plate- and rod-shaped grains. Studies of dielectric and electrical properties of the material were investigated within a wide range of temperature (25–400 °C) and frequency (1 kHz–1 MHz) using complex impedance spectroscopic method. The observation of hysteresis loop of the material confirmed that the material has a ferroelectric property at room temperature. The ac conductivity suggests that the sample obey Jonscher’s universal power law. The dc conductivity follows Arrhenius equation. Detailed studies of ac and dc conductivity show a negative temperature coefficient of resistance (NTCR) behavior of the sample.     

Effect of Sr substitution on structural,dielectric, magnetic and magnetoelectric properties of rapid liquid sintered BiFe0.8Ti0.2O3 ceramics

Structural, dielectric, magnetic and magnetoelectric properties of polycrystalline Sr doped BiFe_0.8Ti_0.2O₃ ceramics [Bi_1?xSr_x(Fe_0.8Ti_0.2)O₃; x = 0.05, 0.10 and 0.15)] were studied. All the samples were prepared by rapid liquid phase sintering method. Rietveld refinement of X-ray diffraction patterns of all samples confirmed that the samples crystallize in a rhombohedral structure and showed change in Fe–O–Fe bond angle and Fe–O bond length which in turn enhanced magnetization from 0.33 to 0.73 emu/g with the increase in Sr concentration from x = 0.05 to 0.15. The dielectric constant and dielectric loss were observed to increase with the increase in temperature from 30 to 500 °C. An anomalous peak has been observed in dielectric constant versus temperature plot around 300 °C for all the samples, which is close to the magnetic transition temperature of BiFeO₃. The composition-dependent magnetic properties with the expected Fe²⁺/Fe³⁺ ratio fluctuations were correlated by X-ray photoelectron spectroscopy. Magnetic and electric hysteresis loops showed a systematic increase in magnetization and polarization as a result of Sr doping in BiFe_0.8Ti_0.2O₃ ceramics. The value of magnetocapacitance at 10 kHz was observed as 0.95, 1.23 and 1.73 for x = 0.05, 0.10, 0.15 respectively in Bi_1?xSr_xFe_0.80Ti_0.20O₃ ceramics.     

Transitions of barium strontium titanate ferroelectric ceramics for different strontium content

Ceramic based barium strontium titanate (BST) solid solutions with the formula Ba_1 − xSr_xTiO₃ 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.     

Effect of dopant concentration on the structural, electrical and optical properties of Mn-doped ZnO films

The Mn-doped ZnO (Zn_1 − xMn_xO) thin films with manganese compositions in the range of 0-8 at.% were deposited by radio-frequency (RF) magnetron sputtering on quartz glass substrates at room temperature (RT). The influence of Mn concentration on the structural, electrical and optical properties of Zn_1 − xMn_xO films has been investigated. X-ray diffraction (XRD) measurements reveal that all the films are single phase and have wurtzite structure with (002) c-axis orientation. The chemical states of Mn have been identified as the divalent state of Mn²⁺ ions in ZnO lattice. As the content of Mn increases, the c-lattice constant and the optical band gap of the films increase while the crystalline quality deteriorates gradually. Hall-effect measurements reveal that all the films are n-type and the conductivity of the films has a severe degradation with Mn content. It is also found that the intensity of RT photoluminescence spectra (PL) is suppressed and saturates with Mn doping.