Room Temperature Dielectric Constant Research Articles

Dielectric, electric, and magnetic response of modified bismuth ferrite-based double perovskites for NTC-thermistor application

Owing to the variation of the characteristics due to the cationic substitution of diverse elements at both A and B sites, the new polycrystalline double perovskite BaBiFeMnO6, synthesized via a cost-efficient solid-state reaction route. Initial structural refinement by Rietveld analysis reveals material crystallised in dual phases i.e. monoclinic and orthorhombic. The respective cell parameters for monoclinic as well as orthorhombic phases are a = 5.5881 Å, b = 5.6541 Å, c = 7.9186 Å with cell angles α = γ = 900 and β = 89.90810 and a = 5.4807Å, b = 5.3583Å, c = 7.4045Å and refined angles are α = β = γ = 900 respectively. The microstructural interpretation of the present sample reflects a non-uniform distribution of the grains with an average grain size of 2.97 μm with a mean crystalline size of 342.65 nm. The Fourier-Transform Infrared Spectroscopy (FTIR) graph indicated that the sample belongs to the perovskite family. The impedance measurement was carried out in a selected frequency and an assigned temperature range to investigate the electrical features of the material which suggested the non-Debye type relaxation and negative temperature coefficient of resistance (NTCR). Furthermore, the thermistor constant (β) and temperature coefficient of resistance (TCR) contributed to investigating the NTCR characteristic of the sample under NTC-type thermistor applications. The room temperature dielectric constant is 1707.67 with a minimal tangent loss of 0.7069 at 100Hz frequency has been estimated by fitting the dielectric data by utilizing the Havrilliak-Negami function. The polarization (P) induced due to the maximum applied electric field of 1.287 kV is studied from the hysteresis loop plotted between them. The hysteresis loop indicates the ferroelectric property of the material with a lossy nature. The room temperature remnant magnetization (2Mr) of 0.4424 emu/g and coercivity (2Hc) of 6.2 kOe have been estimated from the M ∼ H loop. The potentiality of the material to be used as a viable candidate in various energy storage devices and supercapacitors is suggested by all of the characterisations in conjunction with the high value of εr i.e. ∼80000 at 300 °C for the lower frequency.

Low temperature relaxor behaviour of SrBi1.5La0.5Nb2O9 ceramics

Bismuth layered compound with the composition SrBi1.5La0.5Nb2O9 has been prepared using conventional solid-state reaction method. Crystallographic planes have been identified using X-ray diffraction studies. The dielectric studies have been done as a function of frequency and temperature. Low temperature dielectric measurement shows phase transition in which peak dielectric constant shifts from 260K to 280K with the increase in frequency from 1 kHz to 1 MHz. Room temperature dielectric constant has been found to be nearly frequency independent for this composition making it a potential candidate for the capacitor applications. The prepared ceramic was modelled using the Vogel – Fulcher relationship.

High magnetoelectric coupling in piezoelectric modified BNT and magnetic NZFO particulate composite

Lead-free magnetoelectric (ME) particulate composite comprising piezoelectric 72.5Bi0·5Na0·5TiO3-22.5Bi0·5K0·5TiO3–5BiMg0·5Ti0·5O3 (MBNT) and piezomagnetic Ni0·7Zn0·3Fe2O4 (NZFO) in varying phase fraction, i.e., (1-x)MBNT-xNZFO (x = 0.05–0.30; Δx = 0.05) was prepared by solid state reaction route. Their structural, electrical, magnetic and ME properties were investigated. The high temperature sustainability up to 390 °C and the relaxor behavior was confirmed by their dielectric study. The room temperature dielectric constant (∼1081 at 1 kHz), saturation polarization (∼37.12 μC/cm2) and electro-strain (∼0.22 %) was observed maximum for pure MBNT, which decreases in composites with the induction of non-ferroelectric NZFO content. All composites exhibited magnetic hysteresis behavior where net increase in magnetization was associated with the relative increase in NZFO that possessed a saturation magnetization of 74.52 emu/g. At the optimum phase fraction of composite (i.e., 0.80MBNT-0.20NZFO), giant ME coefficient (∼58.12 mV/cm.Oe at 800 Oe) was observed at low frequency of 10 Hz, which suggest its credibility for energy harvester.

Impact of the change in charge compensation mechanism on the electrical, dielectric, and structural properties of La-doped BaTiO3 ceramics

La-doped BaTiO3 ceramics are essential materials in electronic devices, finding applications in multilayer ceramic capacitors and positive temperature coefficient thermistors. While the electrical properties of La-doped BaTiO3 have been investigated, the impact of its room-temperature resistivity anomaly on dielectric properties remains unclear. We synthesized pristine and La-doped BaTiO3 (0.1 – 0.5 mol%) powders via hydrothermal methods, and then sintered bulk samples. Their resistivities (DC and AC), Curie temperature, room-temperature dielectric constant, and lattice volume with varying La doping concentrations were characterized. Beyond 0.3 mol%, the shift from electronic to ionic charge compensation mechanisms resulted in abrupt changes in resistivities, Curie temperature, and dielectric constant near 0.3 mol%. Given minimal changes in average grain size and relative density near 0.3 mol% La, the dominant factor influencing the dielectric constant peaking near this concentration was the shift in charge compensation mechanism.

Engineering DyCrO3 ceramics toward room-temperature high-κ dielectric applications

The search for a high-κ dielectric material that combines a high dielectric constant (ϵ′) and low dielectric loss is very crucial because of its widespread use in gate dielectrics to avoid the leakage current that arises due to continued miniaturization of present SiO2-based metal-oxide semiconductor field-effect transistor devices. RCrO3 (R is a rare-earth ion) materials have been at the center of interest because of their intriguing ferroelectric and magnetic properties, as well as their room-temperature colossal dielectric constant (CDC) values. Although CDC (ϵ′∼104) in RCrO3 materials is quite common, it is unsuitable for device applications since it is associated with a larger dielectric loss value (tan δ∼7 at 11 kHz). Here we have focused on polycrystalline DyCrO3, prepared using multiple synthesis techniques, and thoroughly investigated the origin and tuning of the various dielectric relaxations that give rise to CDC and large dielectric loss values. A clear understanding of the origin of dielectric relaxations enables us to design a specially synthesized DyCrO3 (SPS-DCO) in which the extrinsic dielectric relaxations driven large dielectric loss values can be completely suppressed and which is found to be associated with optimized high-κ dielectric properties [ϵ′∼130, tan δ∼0.06, and temperature coefficient of dielectric constant (TCϵ) ∼ 2280 ppm/K at 11 kHz, 300 K]. The only remaining intrinsic Debye-type dielectric relaxation in SPS-DCO arises due to electric-field-assisted charge hopping among various valences of Cr (investigated using x-ray photoelectron spectroscopy) that presently limits the lowest attainable loss value.

Reinforced energy storage performance of poly(vinylidene fluoride) composite films by filling with surface fluorinated one-dimensional barium titanate nanofibers

One-dimensional barium titanate nanofibers/poly(vinylidene fluoride) (PVDF) composite films were prepared by casting technology. To improve the dispersion of nanofibers in the PVDF matrix and enhance the interface bonding between nanofibers and the PVDF matrix, surface modification of nanofibers was obtained by fluorination treatment. Experimental and theoretical simulation studies were conducted to investigate the effects of surface fluorination-modified one-dimensional barium titanate nanofibers on the micro morphology, structure, dielectric constant, and energy storage density of PVDF composite films. The results showed that the barium titanate powder synthesized by electrospinning had a good one-dimensional fiber morphology, with a diameter of 70–130 nm and a length of 4–15 µm. The surface fluorination treatment was able to significantly improve the dispersion and bonding of the one-dimensional barium titanate nanofiber in the PVDF matrix. As the filling volume of the one-dimensional nanofibers increased, the dielectric constant of the PVDF composite film significantly increased. When the filling volume of the surface fluorinated one-dimensional barium titanate nanofiber was 7.5 vol%, the room temperature dielectric constant of the PVDF composite film reached 21.8, and the surface fluorinated one-dimensional barium titanate nanofiber/PVDF composite film exhibited lower dielectric loss and high breakdown strength. When the filling volume of the surface fluorinated one-dimensional barium titanate nanofiber was 2.5 vol%, the energy storage density of the PVDF composite film was 7.9 J/cm3, which was 2.82 times that of pure PVDF. The improvement of energy storage performance can be attributed to the good dispersion of the surface fluorinated barium titanate nanofibers in the PVDF matrix and the good interface situation. Finite element simulation further revealed that the surface fluorinated one-dimensional nanofibers could effectively improve the breakdown strength of the composites. That provides a promising way to enhance the dispersion and interface bonding of filler in polymer matrices, thereby achieving high-performance composites with high dielectric constant, high breakdown strength, and excellent energy storage density.

High-Performance [00l]-Textured BiAlO3-Doped K0.5Bi0.5TiO3 Ceramics

[00l] grain-oriented 0.95K0.5Bi0.5TiO3–0.05BiAlO3 (named K5BA-T) ceramics were prepared via the reactive template grain growth (RTGG) and tape casting technique. High-aspect-ratio K5BA powder was prepared using a plate-shape 4-layer aurivillius oxide (K0.5Bi4.5Ti4O15) powder as the template. The effects of grain morphology modification and texturing on the structural, dielectric, and piezoelectric properties of K5BA-T were systematically investigated. The average plate size of ∼6.5 μm with a thickness of ∼400 nm was observed in the K5BA sample. X-ray diffraction (XRD) and bulk texture measurements confirmed the texturing of K5BA-T in the [00l] crystallographic direction with a calculated Lotgering factor of ∼80%. Two anomalies in the temperature-dependent dielectric plot of the poled K5BA-T sample signified additional poling-induced phase transition. A lower value of room-temperature (RT) dielectric constant (εr) of ∼ 200 (at 1 MHz) and a higher piezoelectric charge coefficient (d33) of ∼145 pCN–1 were obtained in the poled K5BA-T ceramic compared to that of the 0.95K0.5Bi0.5TiO3–0.05BiAlO3 ceramic with randomly oriented grains (named K5BA-R). Consequently, the piezoelectric voltage coefficient (g33) estimated for the textured ceramic showed a 650% increment (g33 ∼ 80 × 10–3 V mN–1) over the K5BA-R sample (g33 ∼ 12.5 × 10–3 V mN–1). The transduction coefficient (d33·g33) of K5BA-T ceramic was calculated to be ∼11 600 × 10–15 m2 N–1, which is nearly 9 times higher compared to its random counterpart. Further, a piezodevice fabricated using poled ceramic for energy harvesting showed an output voltage of ∼7 V with a current response of ∼2 μA under normal finger-tapping motion.

Room temperature magneto-dielectric coupling in the CaMnO3 modified NBT lead-free ceramics

The sol–gel prepared (1-x)Na0.5Bi0.5TiO3-(x) CaMnO3 (x = 0, 0.03, 0.06, 0.12) compositions show a Rhombohedral (R3c) phase up to x = 0.06 while a mixed rhombohedral (R3c) and orthorhombic (Pnma) phases for the x = 0.12. The lattice volume consistently decreased with an increase in the CaMnO3 content. The phase transition temperature (Tc) decreased with an increase in the CaMnO3 compositions. The room temperature dielectric constant increased, and loss decreased for the x = 0.03 composition due to a decrease in the oxygen vacancy and Bi loss confirmed by the valence state study (XPS). All the compositions show a variation of the room temperature dielectric property with an application of magnetic field confirming a magnetodielectric coupling. The x = 0.06 composition shows the highest negative magnetodielectric coupling constant (MD%) of 3.69 at 100 kHz at an applied field of 5 kG.

Investigation of structural, morphological, and dielectric properties of BaSnO3 ceramics and thin films prepared by sol-gel method

This work intends to compare the structural, morphological and frequency (20 Hz–1 MHz) and temperature (30 °C–300 °C) dependent dielectric properties of BaSnO3 ceramics and thin films. The BaSnO3 solution was prepared by sol-gel method. Thin films were deposited by spin-coating on Pt/Ti/SiO2/Si substrates. The ceramics were prepared with powder derived from the sol-gel solution. X-ray diffraction spectra of ceramics and thin films showed a pure BaSnO3 phase with a cubic structure. The effect of sintering temperature was studied to obtain a good crystalline quality of BaSnO3 ceramics. SEM photos were taken both on ceramics and films. An average roughness of 1.8 nm measured by AFM on films clearly indicates the high quality of the film surface. The phase purity and chemical composition were further confirmed by using energy dispersive X-ray spectroscopy. The room temperature dielectric constant (ε′) was found to be ∼17 and 13 at 1 MHz for ceramics and thin films, respectively. Moreover, quite low dielectric loss tangent values were obtained both for ceramics and thin films. The dielectric study in function of temperature showed maximums on the ε’ evolution at 230 °C and 220 °C, for ceramic and thin film, respectively. XRD patterns taken at different temperatures have shown a stable cubic structure of BaSnO3 powder. This structural stability clearly demonstrates that peaks observed on the temperature dependent plots are only related to dielectric phenomena, which have been described. AC conductivity showed an influence of electrically activated charge carriers, both for ceramics and thin films. The present study also signifies that the dielectric properties of BaSnO3 ceramics can be successfully replicated on thin films by a facile and cost-effective deposition method.

Evidence of direct and converse magnetoelectric coupling in eco-friendly 0.75(0.94Na0.5Bi0.5TiO3-0.06BaTiO3)–0.25(CoFe2O4) particulate composite

Magnetoelectric (ME) multiferroic composite exhibits the ME effect, and their interaction between piezoelectric and magnetic phase is measured in terms of ME coupling (α). ME coupling is an interesting and characteristic property of ME materials and can be evaluated by direct and indirect methods. In this work, the solid-state sintering technique has been adopted to synthesize the lead-free 0.75(0.94Na0.5Bi0.5TiO3-0.06BaTiO3)–0.25CoFe2O4 (NBBT-CFO) composite. The X-ray diffraction patterns and uniform distribution of closely packed grains reveal the coexistence of constituent phases in the composite. This composite reveals room-temperature multiferroic properties. The room temperature dielectric constant (ε′) of the poled sample displays the resonance and anti-resonance peaks at a particular frequency ∼ 455 kHz and 450 kHz, respectively. The estimated value of the electromechanical coupling coefficient (kP) is 16.69%. The direct ME and converse ME coupling study has been done through the Polarization (P) vs Electric field (E) and Magnetization (M) vs Magnetic field (H) hysteresis loop measurements of magnetically and electrically poled and unpoled samples, respectively. The variation in the polarization and magnetization value reveals the presence of direct and converse ME coupling in the composite.

Tailoring magnetic and dielectric properties of Yb2Ti2O7 pyrochlore through structural distortion

While the unique geometrical frustration of pyrochlore Yb2Ti2O7 has attracted attention, the dielectric and other properties of this pyrochlore beyond frustrated magnetism are not well understood. Here, we report on the fascinating low-temperature dielectric relaxation of Yb2-xBaxTi2O7-δ (x = 0–0.20) and demonstrate that this phenomenon is related to structural distortion. A-site Ba substitution, which increases the density of point defects and introduces a different atomic radius, enhances the chemical disorder and structural distortion. As a result, the increases in oxygen vacancies and nonmagnetic Ba2+ and Yb2+ ions dilute the ferromagnetic Yb3+–Yb3+ interactions, as indicated by the decrease in effective magnetic moment. On the other hand, the distorted octahedra facilitate the hopping of Yb ions, and the random distribution of Ba2+ ions at the Yb3+ sites gives rise to additional random fields, leading to significantly increased dielectric relaxation. The room-temperature dielectric constant is improved to ∼170, twice that of pristine Yb2Ti2O7. This work provides a comprehensive view of the structural, magnetic, and dielectric properties of Yb2Ti2O7 and lays the foundation for additional research into pyrochlore compounds.

Effect of Gd3+/Ti4+ heterovalent substitution on the crystal structure, morphology, optical properties, and phase transition behavior of bismuth layer-structured SrBi2Nb2O9

The double-layer Aurivillius compounds Sr1-xGdxBi2Nb2-xTixO9 (x ​= ​0, 0.2, 0.4, 0.6, 0.8, and 1), which have the potential to be developed as a ferroelectric material, have been synthesized using the molten salt method. This study aims to investigate the effect of the simultaneous substitution of Gd3+ and Ti4+ ions in SrBi2Nb2O9 on the phase formation, crystal structure, morphology, and ferroelectric properties. The single-phase product with A21am orthorhombic structure was obtained for all samples by X-ray diffraction analysis. The unit cell becomes more orthorhombic with increasing x as the degree of tetragonality increases. SEM micrographs demonstrate the plate-like grain morphology with an anisotropic growth direction, and the grain is smaller in size with increasing x. FTIR spectra indicate that cation substitution was successful, especially Ti4+ ions at the B-site. With increasing x, the ferroelectric transition temperature (Tc) increases, which has been explained in terms of a reduction in the tetragonality. The open hysteresis loops provide evidence of ferroelectric properties which is consistent with the trend of room-temperature dielectric constant. The optical bandgap value is proportional to the trend of the dielectric characteristics of the samples.

Structural, Dielectric and Ferroelectric Characterizations of Sol-gel Prepared Ba1-xSrxTiO3 Nanoceramics

Ba1-xSrxTiO3 (0.0 ≤ x ≤ 0.5) nanoceramics were synthesized via sol-gel route and the structural and electric properties of the resulting compositions were investigated. revealed A tetragonal crystal structures for x = 0.0 - 0.3 and a cubic structure for x = 0.5 compositions was revealed by X-ray diffraction. The smaller ionic radii of Sr ions resulted in the lowering of c/a ratio with increasing x and a tetragonal to cubic structural transformation was observed at around x = 0.4. The average crystallite size gradually decreased with increasing x from 0 to 0.5. This trend was visible in electron micrographs. The room temperature dielectric constant in these nanoceramics increases with increasing Sr and a maximum value of 1553 was observed for x=0.3. Curie temperature (Tc ) of 125 °C was obtained for x=0.0, which shifted toward lower temperature with increasing x value. The value of Tc was observed as 100 and 75 °C for x = 0.1 and 0.3, respectively. The remnant polarization (Pr ), saturation polarization (Ps ), and coercive field (Ec ) decreased with increasing Sr concentration in BT due to the structural modifications. Value of Pr decreases from 0.637 to 0.229 μC/cm2, Ps decreases from 8.910 to 3.238 μC/cm2 and Ec decreases from 0.631 to 0.255 kV/cm with increasing x from 0 to 0.5.

Structural, optical dielectric and ferroelectric properties of double perovskite BaBiFeTiO6

The polycrystalline BaBiFeTiO6 (BBFTO) ceramic is synthesized by a high-temperature solid-state reaction route. According to X-ray Diffraction (XRD) and Rietveld refinement analysis, the compound is cubically ordered and belongs to the Fm-3 m space group. The universal Scherrer's formula was used to calculate the average crystallite size of 55 nm. Scanning electron micrographs (SEM) show non-uniform distributions of dense micro grains of average grain size of 150 nm. Tauc equation and diffuse reflection spectra were used to determine the absorbance and reflectance optical bandgap as 2.15 eV and 2.25 eV, which supports the possible usage in photocatalytic applications. The P-E hysteresis loop revealed the compound has room temperature (RT) ferroelectric property with higher remnant polarization, 2Pr = 1.93µC/cm2, thus can be useful in ferroelectric memory devices. The material experiences ferroelectric to a paraelectric phase transition, Td > 410 °C, Curie point, Tc > 490 °C and RT dielectric constant, ɛr = 1149 at 100 Hz, hence can be used as a dielectric material in multi-layered ceramic capacitors.

Yttrium doping induced modifications in the electrical properties of cobalt zinc ferrite

Yttrium doped cobalt zinc nano-ferrites Co0.8Zn0.2Fe2-xYxO4 (x = 0, 0.01, 0.02, 0.03) were synthesized through the combustion method. For the formation and confirmation of single phase cubic spinel structure, X-ray diffraction is used. The average grain sizes from the Scherrer formula were below 50 nm. Microstructural features were obtained by scanning electron microscope. Electrical properties, such as dc resistivity as a function of temperature and ac conductivity as a function of frequency were studied for these samples. Room temperature dielectric constant (ε′) and dielectric loss (tan δ) are also studied as a function of frequency. The differentiation of dielectric properties ε′, tan δ, and ac conductivity (σac) with frequency imparts that the dispersion is because of Maxwell–Wagner type of interfacial polarization in general and the hopping of charge between Fe2+ and Fe3+ as well as Co2+ and Co3+ ions at B-sites. Electrical property study showed its dependence on the grain size.

Effect of pH value on multiferroic properties of barium ferrite ceramics prepared by sol–gel method

In this paper, BaFe12O19 (BaM) ceramics at different pH values were prepared by sol–gel method. Effects of pH value on the microstructure, electrical as well as magnetic properties were systematically studied. XRD indicate that the ceramics were mainly BaM. However, with the pH value increasing further, the BaFe2O4 impurity phase appears gradually in both powders and ceramics due to the degree of complexation between citric acid and metal cations and other reasons. SEM results show that the grain size of ceramics decreases from 2.28 μm to 1.35 μm with the pH value increase from 4 to 8. It is found that room temperature dielectric constant, residual polarization, and saturation magnetization of the ceramics is the largest when the pH value of the solution is 4, which are 0.108 μC/cm2 and 32.829 emu/g, respectively. The dielectric constant and residual polarization of ceramics decrease with the increase of pH value. The ferroelectric and magnetic hysteresis loops have confirmed room-temperature multiferroic properties of the prepared ceramics. It laid the foundation for the further development of new room temperature single-phase multi-iron materials.

New superdielectric materials: (1-x) SrFe12O19 – x BNT-BT nanocomposites

Novel (1-x) SrFe12O19 – x BNT-BT0.08 (x = 0; 0.5; 0.8; 1) nanocomposites were explored in this study. The samples were produced by sol-gel method and compacted by conventional sintering. The composition, morphology, local structure, dielectric and magnetic properties were investigated by X-ray diffraction, Transmission Electron Microscopy, Impedance Analysis, Mössbauer spectroscopy, and SQUID magnetometry. The desired composition and the presence of the magnetoplumbite SrFe12O19 and perovskite BNT-BT structures were verified by X-ray diffraction. Irregular morphology and large size distributions are evidenced in the electron microscopy micrographs. The reported room temperature dielectric constants in this study are the highest values obtained in multiferroic composites at room temperature: giant dielectric constants (∼1.3 × 106) were obtained, relative to 0.13 × 104 in BNT-BT. The hyperfine parameters allowed the identification of the Wyckoff positions of the Fe ions corresponding closely to the theoretical case. The hard magnetic character of the SrFe12O19 phase is evidenced from the magnetic measurements. For the first time in multiferroic composites, superdielectric characteristics are evidenced at room temperature.

NaNbO3 modified BiScO3-BaTiO3 dielectrics for high-temperature energy storage applications

Among the lead-free compositions identified as potential capacitor materials, BiScO3-BaTiO3 (BS-BT) relaxor dielectrics exhibit good energy storage performance. In this research, 0.4BS-0.6BT is considered as the parent composition, with NaNbO3 (NN) addition intended to substitute the A and B site cations. The NN modified BS-BT ceramics exhibit excellent temperature stability in terms of their dielectric properties, with the room-temperature dielectric constant on the order of 500–1 000 and variation less than 10% up to 400 °C. In addition, NN has a high band-gap energy leading to increased breakdown strength and energy storage properties in modified compositions. The highest breakdown strength was achieved for 0.4BS-0.55BT-0.05NN, being on the order of 430 kV/cm, and a high energy density of 4.6 J/cm3 with high energy efficiency of 90% was simultaneously achieved. Of particular importance is that the variation of the energy density was below 5% due to the temperature-insensitive dielectric constant, while ∼90% energy efficiency was retained over the temperature range of 25–160 °C. The improved temperature stability with NN addition makes this composition promising for high temperature capacitor and dielectric energy storage applications.

Improved dielectric and piezoelectric properties of Sm-doped Pb(Mg1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)-PbTiO3 ternary ferroelectric ceramics

Sm-doped Pb(Mg1/3Nb2/3)-PbTiO3 (PMN-PT) binary ferroelectric ceramics has received extensive attention due to the excellent dielectric and piezoelectric properties. However, its Curie temperature (Tc) is greatly reduced by Sm doping and Tc is only 89 °C at the optimum piezoelectric coefficient. In this work, Sm-doped Pb(Mg1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)-PbTiO3 (Sm: PMN-PZN-PT) ternary ferroelectric ceramics near MPB were successfully manufactured and the crystal structure, microstructure and electric properties were investigated with respect to Sm doping content. A high piezoelectric coefficient of 870 pC/N and a high Tc of 146 °C were achieved simultaneously in PMN-PZN-PT ternary ceramics with 1% Sm doping content. In addition, the room temperature dielectric constant was greatly improved by Sm doping and the Pr, Ps and Ec values gradually decrease with the increase of Sm content. These results indicate that Sm-doped PMN-PZN-PT ceramics may be an attractive material for high performance piezoelectric device applications.

Dielectric Properties of Colossal-Dielectric-Constant Na1/2La1/2Cu3Ti4O12 Ceramics Prepared by Spark Plasma Sintering.

In the current study, we report on the dielectric behavior of colossal-dielectric-constant Na1/2La1/2Cu3Ti4O12 (NLCTO) ceramics prepared by mechanochemical synthesis and spark plasma sintering (SPS) at 850 °C, 900 °C, and 925 °C for 10 min. X-ray powder diffraction analysis showed that all the ceramics have a cubic phase. Scanning electron microscope observations revealed an increase in the average grain size from 175 to 300 nm with an increase in the sintering temperature. SPS NLCTO ceramics showed a room-temperature colossal dielectric constant (>103) and a comparatively high dielectric loss (>0.1) over most of the studied frequency range (1 Hz–40 MHz). Two relaxation peaks were observed in the spectra of the electrical modulus and attributed to the response of grain and grain boundary. According to the Nyquist plots of complex impedance, the SPS NLCTO ceramics have semiconductor grains surrounded by electrically resistive grain boundaries. The colossal dielectric constant of SPS NLCTO ceramics was attributed to the internal barrier layer capacitance (IBLC) effect. The high dielectric loss is thought to be due to the low resistivity of the grain boundary of SPS NLCTO.