TiO3 Samples Research Articles

Determination of the Activation Energy of Defects in Ferroelectrics by the Method of Temperature Activation–Relaxation of the Dielectric Permittivity

The article proposes a method of temperature activation–relaxation of the permittivity for determining the activation energy of defects in ferroelectrics using lead zirconate–titanate Pb(Zr,Ti)O3 samples as an example. This method is based on the analysis of relaxation of the permittivity after thermal annealing and the analysis of the temperature activation of the permittivity of the Pb(Zr,Ti)O3 ferroelectric. The equality of the activation energy corresponding to the process of migration of oxygen vacancies and the thermal energy of the decay of the domain structure was established, which was confirmed by studying the surface of the samples by scanning electron microscopy. When this temperature was reached, the surface of the domain walls was detached from oxygen vacancies, which are pinning centers. This manifested itself in photographs of the microstructure as a change in the ordering of the domains emerging on the surface of the sample, which led to an irreversible decrease in the permittivity of the sample. For the obtained activation energies, the physical process of domain wall motion activation is established, which is determined by their pinning on structural defects (oxygen vacancies). It is assumed that the irreversible decay of the domain structure occurs when the domain walls are displaced by distances exceeding the elementary lattice parameter of the ferroelectric. The proposed method can be part of a comprehensive study that includes electrophysical, microscopic and X-ray methods.

Graphite sintered strontium praseodymium titanate perovskite for thermoelectric applications

Here Pr3+ was introduced in the Sr2+ site in Sr1-x PrxTiO3 (x = 0.05, 0.075, 0.10, 0.125, 0.15, 0.20) system followed by two step graphite burial sintering. Powder reduction helps to increase the carrier concentration and the doped sample pellet reduction minimizes Double Schottky Barrier generated by strontium and oxygen vacancies at grain boundary by regulating the point defects. Samples with x ≥ 0.10 shows splitting and asymmetry of (200) and (310) peak in XRD indicating structural transformation from cubic to tetragonal phase. XPS spectra of the samples confirmed the formation of oxygen vacancies and reduction of Ti4+ to Ti3+ induced by graphite burial sintering resulting in enhanced carrier concentration. A maximum power factor of 1.8 mW/mK2 was obtained for Sr0.9 Pr0.1TiO3 samples at 673 K. Reduced thermal conductivity due to porous structure, Pr defect centers, oxygen vacancy clusters together with enhanced power factor lead to a maximum figure of merit 0.33, making this an ideal candidate as n type legs in thermoelectric generators.

Tailoring the structural and optical properties of lead-free Na0.5(Bi1-xSmx)0.5TiO3 multifunctional ceramics by Sm-doping

In this study, the effects of Sm3+-content on the structural and optical properties of the Na0.5(Bi1-xSmx)0.5TiO3 multifunctional lead-free system were investigated using x-ray diffraction (XRD), ultraviolet-visible (UV-Vis), Raman spectroscopy and photoluminescence (PL) spectroscopy. The Na0.5(Bi1-xSmx)0.5TiO3 (x = 0.000, 0.005, 0.010, 0.015, and 0.020) ceramics were synthesized by the solid-state reaction method with subsequent annealing. The Rietveld method was used to refine the XRD data. The results of these refinements indicated that pure NBT (Na0.5Bi0.5TiO3) and the Sm3+-doped samples showed the coexistence of the rhombohedral (R3c) and tetragonal (P4bm) phases in different fractions, which depend on the Sm3+-content. The UV-Vis data revealed that the optical band gap of the Na0.5(Bi1-xSmx)0.5TiO3 samples monotonically decreases with increasing Sm3+-content, providing evidence of replacement of Bi3+- by Sm3+-ions. Furthermore, Raman spectroscopy confirmed that substitution of Bi3+- by Sm3+-ions leads to a shortening of the Na/Bi-O bond length. It was demonstrated that this behavior is responsible for the increase in the local symmetry of the TiO6 octahedron and the consequent decrease in the ratio between both rhombohedral and tetragonal phases, as observed by the XRD data. The findings from the PL data revealed typical emissions corresponding to transitions between the 4G5/2 → 6Hj (j = 5/2, 7/2, 9/2, 11/2, 13/2) states of the Sm3+-ion. Additionally, the presence of non-radiative recombination processes was found to depend on both laser pumping power and Sm3+-content.

Field-induced structural and orbital transformations leading to large bulk photovoltaic response in modified barium titanate

Ferroelectric systems are gaining importance in the perspective of capitalizing on their potential in energy applications. In particular, the ferroelectric photovoltaic effect is one of the attractive fields because of the reported above bandgap photovoltage. Although numerous efforts are being made to understand the ferroelectric photovoltaic mechanism, correlations among the structural, orbital, and photovoltaic characteristics, useful to engineer the system for applications, are rarely being investigated. Here, such correlations are established in electric field-induced studies carried out on the lead-free ferroelectric Ba0.875(Bi0.5Li0.5)0.125TiO3 system. Upon poling, x-ray diffraction studies reveal a twofold enhancement in the orthorhombic phase fraction at the expense of the tetragonal phase in comparison with the unpoled sample. The ex situ and in situ Raman studies demonstrate the field-induced changes in the structural characteristics. Furthermore, the Rayleigh analysis validates the field-induced lattice deformation in accordance with x-ray diffraction and Raman studies. Notably, the Ba0.875(Bi0.5Li0.5)0.125TiO3 sample exhibits anomalous open-circuit voltage (12 V) under the poling condition. To substantiate the experimental finding, density functional theory calculations are carried out. The theoretical calculations elucidate that the conduction band edge of the orthorhombic phase has a vital contribution from z character orbitals, which is further enhanced under poling to give rise to a higher shift current and, hence, a better photovoltaic response. However, the tetragonal phase's orbital characters are robust upon poling. Overall, these studies pave the way for designing ferroelectric systems for better photovoltaic properties.

Structural, thermal properties and improved ionic conductivity of cerium-doped Li0.5+xLa0.5-xCe2xTi1-xO3 solid electrolyte materials

A series of Ce-doped Li0.5+xLa0.5-xCe2xTi1-xO3(x = 0.0, 0.025, and 0.05) ionic conductive crystalline oxides were produced by a solid-state reaction process. The effect of Ce-doping on the thermal, structural, electrical, and dielectric characteristics of Li0.5La0.5TiO3 was investigated using TGA/DTA, XRD, SEM/EDS, FT-IR spectroscopy, and impedance spectroscopy techniques. The TGA/DTA spectra confirmed the phase transformation and weight loss of the mixed precursors. The XRD and FT-IR analysis revealed that the materials exhibited a cubic system with a perovskite phase, which corresponds to the Pm3m space group. The EDS analysis clearly detected the presence of all elements except Li in the Li0.5+xLa0.5-xCe2xTi1-xO3 materials. The electrical conductivities were found to be 3.9 × 10−5 S/cm for Li0.525La0.475Ce0.05Ti0.975O3, and 3.1 × 10−5 S/cm for Li0.55La0.45Ce0.1Ti0.95O3, which are higher than that of Li0.5La0.5TiO3 (1.7 × 10−5 S/cm). This confirmed that the incorporation of a small quantity of Ce4+ ions can enhance the electrical conductivity of Li0.5La0.5TiO3 sample.

High-Temperature Dielectric Relaxation and Electric Conduction Mechanisms in a LaCoO3-Modified Na0.5Bi0.5TiO3 System.

This research study examines the high-temperature dielectric relaxation and electric conduction mechanisms in (x)LaCoO3-(1 - x)Na0.5Bi0.5TiO3 samples, where x is 0.05, 0.10, and 0.15. The findings demonstrate that all the samples exhibit two dielectric transitions: first, a frequency-dispersive shoulder at a lower temperature (Ts) around 425-450 K, which is associated with polar nanoregions (PNRs), and second, from ferroelectric to paraelectric transition at the Curie temperature (Tc) approximately between 580 and 650 K. The impedance analysis reveals the negative temperature coefficient of resistance behavior of the specimens. The broad and asymmetric relaxation peaks obtained from modulus spectroscopy demonstrate a wide range of relaxations, suggesting non-Debye-type behavior. Furthermore, the conductivity studies provide insights into understanding the transport phenomena in the samples. The oxygen vacancies resulting from the addition of LaCoO3 into the Na0.5Bi0.5TiO3 ceramics are responsible for the relaxation and conduction processes, and the charge carrier is doubly ionized oxygen ion vacancies. All samples except for LCNBT10 at 1 kHz exhibit a negative magnetodielectric response.

Influence of heat-treatment temperature on structural and electrical properties for BaSrTiO3 compounds

The sol-gel process was utilized in the production of the ferroelectric material Ba0.7Sr0.3TiO3. Barium and strontium acetate were employed as sources for Ba and Sr, respectively, and Ti(IV) isopropoxide was used as a source for Ti. The acetic acid was utilized as a solvent for Ba and Sr acetate, whereas 2-methoxy ethanol was used as a stabilizer for Ti (IV) isopropoxide. The effect of high temperatures on electrical and structural were studied. The FESEM revealed the particle size of all samples with different temperatures. The XRD shows the Ba0.7Sr0.3TiO3 samples have a tetragonal phase for all temperatures (1000, 1100, 1200˚C). The high temperatures impacted tetragonality and the lattice constant (a, c); the lattice constant decreased at higher temperatures. The ferroelectric sample sintered at 1000 degrees Celsius had dielectric characteristics that were inferior to those of the Ba0.7Sr0.3TiO3sample sintered at 1100 and 1200ºC degrees Celsius. When the dielectric constant was graphed as a function of temperature, the Curie temperature appeared to be between (28-32) degrees Celsius.

In-situ construction of all-scale hierarchical microstructure and thermoelectric properties of (Sr0.25Ca0.25Ba0.25La0.25)TiO3/Pb@Bi composite oxide ceramics

SrTiO3-based oxides have been investigated as a promising n-type thermoelectric material at high temperatures; however, the relatively high thermal conductivity results in inferior thermoelectric performance. The lattice thermal conductivity can be significantly reduced by high-entropy engineering via severe lattice distortion. However, high configuration entropy also causes the deterioration of carrier mobility and restrains electron transport resulting in low electrical conductivity. In this work, the low lattice thermal conductivity of 1.7 W/(m·K) at 1 073 K and significantly improved electrical conductivity of 112 S/cm from 60 S/cm can be achieved in n-type (Sr0.25Ca0.25Ba0.25La0.25)TiO3/Pb@Bi composites ceramics with core-shell grains of all-scale hierarchical microstructure. The effects of the complex microstructure of core-shell grains as well as the precipitated Pb@Bi particles on electrons and phonons transport properties were systematically explored. ZTmax of 0.18 was obtained for the SPS-1200, which was 1.5 times that of pure high-entropy (Ca0.2Sr0.2Ba0.2La0.2Pb0.2)TiO3 samples prepared by a solid-state method. This improvement in thermoelectric performance contributes to the addition of Bi2O3 into the high-entropy (Sr0.2Ca0.2Ba0.2Pb0.2La0.2)TiO3 matrix resulting in multiphase core-shell grain structure combined with well-dispersed nano-sized metal Pb@Bi precipitates in the matrix. This feasible strategy of in-situ constructing all-scale hierarchical nanostructures can also be applied to enhance the performance of other thermoelectric systems.

Structural, electrical, and magnetic properties of Ce and Fe doped SrTiO3

Here, we report on the structural, vibrational phonon, electrical, and magnetic properties of undoped strontium titanate SrTiO3, Ce doped Sr1−xCexTiO3, and (Ce, Fe) co-doped Sr1−xCexTi1−yFeyO3 samples synthesized through solid state reaction route. The Rietveld refined powder x-ray diffraction analysis confirmed the cubic Pm-3m phase in our as-synthesized samples. We observed grain size reduction in SrTiO3 from scanning electron micrographs due to the incorporation of Ce and Fe dopants. The sample purity in terms of chemical species identification has been confirmed from energy-dispersive x-ray spectroscopy. The characteristic phonon modes in our samples are identified using room temperature Raman spectroscopy and benchmarked against existing relevant experimental observations. The incorporation of Ce and Fe as substitutional dopants in SrTiO3 unit cell was confirmed from the absence of absorption at 480, 555, 580, and 1635 cm−1 band in Fourier transform infrared spectra. The 3% Ce doping in Sr0.97Ce0.03TiO3 sample may have induced ferroelectric order, whereas the undoped SrTiO3 (STO) revealed lossy paraelectric nature. In the case of (Ce = 3%, Fe = 10%) co-doped Sr0.97Ce0.03Ti0.90Fe0.10O3 sample, we observed ferromagnetic hysteresis with orders of magnitude enhancement in remnant magnetization and coercivity as compared to undoped STO sample. This long range robust ferromagnetic order may have originated from F-center mediated magnetic interaction.

Room temperature ferroic orders in Zr and (Zr, Ni) doped SrTiO3

We synthesized strontium titanate SrTiO3 (STO), Zr doped Sr1−xZrxTiO3 and (Zr, Ni) co-doped Sr1−xZrxTi1−yNiyO3 samples using solid state reaction technique to report their structural, electrical and magnetic properties. The cubic Pm-3m phase of the synthesized samples has been confirmed using Rietveld analysis of the powder X-ray diffraction pattern. The grain size of the synthesized materials was reduced significantly due to Zr doping as well as (Zr, Ni) co-doping in STO. The chemical species of the samples were identified using energy-dispersive X-ray spectroscopy (EDX). The Zr and Ni dopants’ homogeneity were confirmed from EDX mapping to negate spurious ferroic order due to dopant segregation. We observed forbidden first order Raman scattering at 148, 547 and 797 cm−1 which may indicate nominal loss of inversion symmetry in cubic STO. The absence of absorption at 500 cm−1 and within 600–700 cm−1 band in Fourier Transform Infrared spectra corroborates Zr and Ni as substitutional dopants in our samples. Due to 4% Zr doping in Sr0.96Zr0.04TiO3 sample dielectric constant, remnant electric polarization, remnant magnetization and coercivity were increased. Notably, in the case of 4% Zr and 10% Ni co-doping we have observed clearly the existence of both FE and FM hysteresis loops in Sr0.96Zr0.04Ti0.90Ni0.10O3 sample. In this co-doped sample, the remnant magnetization and coercivity were increased by ∼1 and ∼2 orders of magnitude respectively as compared to those of undoped STO. The coexistence of FE and FM orders in (Zr, Ni) co-doped STO might have the potential for interesting multiferroic applications.

Ultrasound-driven ferroelectric polarization of TiO2/Bi0.5Na0.5TiO3 heterojunctions for improved sonocatalytic activity

Herein, a series of TiO2/Bi0.5Na0.5TiO3 heterojunctions with different mass ratio are first constructed under ultrasound irradiation, which shows superior sonocatalytic and photoelectrochemical properties. The improved performance is attributed to the internal electric field and close interfacial contact of TiO2 and Bi0.5Na0.5TiO3, which promote the transfer of photoinduced electrons from TiO2 to Bi0.5Na0.5TiO3. The spontaneous polarization of ferroelectrics in the heterostructures can be adjusted by ultrasonic treatment durations, which further influences the internal electric field. The TiO2/Bi0.5Na0.5TiO3 sample with mass ratios of 5:1 and ultrasonic treatment for 15 min presents the highest sonocatalytic degradation of Rhodamine B. Moreover, the sonocatalytic activity also shows a close relevant to the ultrasonic temperature and frequency of degradation process. And, the •OH radicals are mainly responsible for Rhodamine B sonodegradation. This work provides a novel TiO2/Bi0.5Na0.5TiO3 heterojunctions and promotes the application of ferroelectrics modified materials in sono-/photo-catalysis.

Nonstoichiometric effect of A-site complex ions on structural, dielectric, ferroelectric, and electrostrain properties of bismuth sodium titanate ceramics

To investigate the nonstoichiometric effect of (Bi0.5Na0.5)TiO3 (BNT) ceramics on their properties, we propose a novel chemical expression, (Bi0.5+xNa0.5−3x)TiO3. The nonstoichiometric effect of BNT can be explored in compounds with this composition without being hampered by the charge imbalance problem. With x ranging from −0.02 to 0.02, we find that the morphological, dielectric, ferroelectric, and electrostrain properties differ considerably between Na-rich and Bi-rich ceramic samples. The average grain size (AGS) increased significantly in Na-rich samples compared to that in stoichiometric BNT, while it decreased slightly in Bi-rich samples. The dielectric characteristics measured from 30 °C to 500 °C indicate that conductivity is activated in Na-rich nonstoichiometric samples but is effectively suppressed in Bi-rich nonstoichiometric samples. The ferroelectric properties also show the same trend. In Na-rich samples, elliptical polarization against electric field (P-E) hysteresis loops were detected, indicating a conductive character induced by high electric field loading. However, saturated P-E loops are observed in Bi-rich samples with well-inhibited conductivity. Furthermore, compared to stoichiometric BNT and nonstoichiometric x = 0.02 Bi-rich samples, (Bi0.5+xNa0.5−3x)TiO3 samples with x = 0.01 exhibit higher electrostrain from 30 °C to 150 °C. Based on the assumption of charge balance, our findings indicated that the presence of 1 mol% excess Bi would facilitate significant improvement in the dielectric, ferroelectric, and electrostrain properties of BNT and BNT-based systems.

Comprehensive characterization of Ba1−xSrxTiO3: Correlation between structural and multifunctional properties

Considering the superior multifunctional performance and beautiful structural tunability, Ba(1−x)SrxTiO3 (0 ≤ x ≤ 1) samples were synthesized in this work by following a conventional solid state reaction technique. The structural, vibrational, optical and dielectric properties of the synthesized materials were characterized extensively throughout the work. Band gap energy of all the materials was evaluated from optical characterizations and correlated with structural properties. Study of leakage characteristics rendered fruitful explanation for electrical properties. At x = 0.4, a structural phase transition from ferroelectric to paraelectric state was observed. All the functional properties were correlated with structural properties. The Ba0.6Sr0.4TiO3 sample showed maximum room temperature dielectric permittivity (~4000 at 1 kHz) with good frequency and thermal stability. The dielectric loss tangent of this composition was reduced to ~0.0098 (at 1 kHz) which was even much lower than that of undoped BaTiO3. The detail temperature dependent dielectric and impedance characteristics of this sample were also evaluated. The activation energy, calculated from dielectric characterizations, was found to be ~1 eV suggesting the governance of doubly ionized oxygen vacancy for conduction and relaxation mechanism.

Evidence on the quantum critical point in EuTiO3–SrTiO3 solid solution

EuTiO3 (ETO) and SrTiO3 (STO) are the two well-known analogous quantum paralelectric materials. In the present study, we synthesized Eu1-xSrxTiO3 for various values of x (0 < x < 1) by solid state reaction method. X-ray diffraction (XRD) measurement performed on the synthesized samples confirmed the cubic structure with tetragonal distortion for Eu rich samples. The phase purity of the synthesized samples was also confirmed by the X-ray measurements. X-ray photoelectron spectra were measured to show that the valence state of Eu is in 2+ states. The dielectric and magnetic properties of Eu1-xSrxTiO3 samples were systematically studied. The dielectric constant against temperature for pure ETO shows sudden drop at Neel temperature 5.3 K confirming the coupling between electric and magnetic polarization. The magnetization value remains constant below the Neel temperature for ETO and Eu0.8Sr0.2TiO3 samples while others show paramagnetic behavior. The magneto dielectric effect shows a huge value of around 5% at 2 K for ETO and abruptly drops by Sr doping. The proposed phase diagram with the magnetic and dielectric data of Eu1-xSrxTiO3 suggests a quantum critical point around the composition of Eu0.7Sr0.3TiO3.

Structural and optical properties of (Y3+, Tb3+)-codoped sodium bismuth titanate nanoparticles

The present study investigates the effect of (yttrium, terbium) ions codoping on structural and optical properties of sodium bismuth titanate (Na0.5Bi0.5TiO3 or NBT) with the possible practical application as a multi-luminescence material in optoelectronic devices such as light-emitting diodes. The polycrystalline samples of Na0.5(Y/TbxBi1-x)0.5TiO3 (x = 0.00, 0.04, 0.06, and 0.08) were synthesized using solid-state reaction (mixed oxide) technique. Stoichiometric amounts of metal compounds (Na2CO3, Y2O3, Tb4O7, Bi2O3, and TiO2) were mixed via ball milling at 250 rpm for 2 h, and the ground powders were calcined at 700 °C for 2 h. The powders were pressed under uniaxial pressure of 6.87 MPa to obtain green pellets, which were later sintered at 1,000 °C for 2 h to obtain the Na0.5(Y/TbxBi1-x)0.5TiO3 samples. X-ray diffraction analysis suggests that the perovskite phase is established for all (Y3+, Tb3+)-codoped NBT compositions (x = 0.00–0.08). The presence of NBT functional groups was confirmed by Fourier transform infrared spectroscopy. Raman spectra indicate that (Y3+, Tb3+) ions induce minor changes to the crystal lattice structure, with no disturbance to the long-range order. X-ray photoelectron spectroscopy results reveal the presence of all the constituent elements in the NBT samples. Scanning electron microscopy confirms the polycrystalline nature of the samples with uniform distribution of multifacetted or nearly spherical grain structures. Transmission electron microscopy and selected area electron diffraction (SAED) images show the presence of nanocrystals in the samples. Ultraviolet diffuse reflectance spectroscopy (UV-DRS) and photoluminescence results illustrate that Na0.5(Y/TbxBi1-x)0.5TiO3 possess wider optical energy band gap (Eg = 3.23–3.27 eV) with promising luminescence applications in the optoelectronic industry.

Effect of sintering temperature on Li diffusivity in Li0.29La0.57TiO3: Local hopping and long-range transport

The influence of sintering temperature on Li diffusivity was investigated for two Li0.29La0.57TiO3 samples sintered at 1400 °C and 1450 °C, respectively. Synchrotron radiation diffraction was used to get detailed insights into the crystal structure and the real structure and also into the subtle differences between the two samples. 7Li NMR relaxometry and 7Li PFG NMR were used to observe the local hopping of Li ions and the long-range transport, respectively. Our results show that the motion of Li ions inside the crystallites is very similar for both samples. The enhanced conductivity of the sample sintered at the higher temperature, as observed by impedance spectroscopy, is caused by the reduced density of grain boundaries.

Magnetic properties of Sm-doped barium titanate (Ba0.99Sm0.01TiO3) prepared by sol–gel route

We report the magnetic properties of Ba0.99Sm0.01TiO3 (BSmT1) sample synthesized through the sol–gel process. The sample consisted of crystallites of nanometric sizes (33.2 nm). The magnetization was measured at different temperatures and different magnetic applied fields using the vibrating-sample magnetometer (VSM) technique. The curves of magnetization versus temperature at different fields showed that the magnetization decreased with temperature and revealed an anomaly between 20 and 75 K, this anomaly became remarkable when the magnetic field (H) increased. The hysteresis loops showed the coexistence of ferromagnetic and antiferromagnetic phases at low temperature (< 20 K). When the temperature increased the ferromagnetic phase that became dominant ( $${20}\,{\text{K}} \le {T} \le {50}\,{\text{K}}$$ ), and above 50 K, we observed the emergence of a diamagnetic order in coexistence with ferromagnetic one. A good fit of the isothermal curves of magnetization, using a modified Brillouin function, was obtained with the value J = 0.5, which was assigned to Sm3+ in its first excited state (6H7/2 multiplet). The thermal behavior of the entropy change ( $${ - }\Delta {\text{S}}_{{M}}$$ ) was in a good concordance with the thermal behavior of the magnetization, which confirmed the obtained results from magnetization versus temperature and from the hysteresis loops.

Structural, electronic and thermoelectric properties of SrTiO3 ceramic doped by lanthanum using first principles

The Sr0.92La0.08TiO3 model compound was studied by means of the first-principles method grounded on the full-potential linearized augmented plane wave with the local orbital method as implement in WIEN2k. The structures, electronic and thermoelectric properties of the model compound are examined. Geometry optimization of Sr0.92La0.08TiO3 compound structure reveals the lattice constant of 3.9451 Å, which is the same as un-doped SrTiO3. The direct bandgap of 2.48 eV (Γ-Γ) was measured from computed electronic band structure and its displayed density of states for Sr0.92La0.08TiO3 sample. Transport properties were calculated using BoltzTraP code as implemented in the WIEN2k code. The results were analyzed as a function of the variable temperatures, the density of state and chemical potential. Temperature and density of state variation with transport properties are in the same trend. Chemical potential proves material as n-type via Seebeck coefficient. The thermoelectric performance ZT of 0.05 was obtained at room temperature, while maximum value of 3.79 was recorded at 1200 K.

Study of thermoelectric properties of Sr0.92A0.08TiO3 (A=Yb / Tm) perovskite oxide using density functional theory method

The first principle methods have been employed to investigate electronic and thermoelectric properties of Sr0.92Yb0.08TiO3 and Sr0.92Tm0.08TiO3 perovskite-oxide based molded samples. Generalized gradient approximation (GGA) with Hubbard U parameter is used by WIEN2k code for the calculations. The straight band line was observed in the band structure of both studied samples. This was generated from 4f-orbitals as shown in partial density of state diagrams. It is also noticed that Yb and Tm doped in SrTiO3 changed the perovskite-based oxide from a wideband insulator to metallic nature. A thermoelectric power factor of Sr0.92Tm0.08TiO3 sample is higher than that of Sr0.92Yb0.08TiO3, this is as a result of its huge electrical conductivity. The dependent of chemical potential to temperature was revealed in the study where high value of power factor was recorded for high temperature.

Study of low temperature-dependent structural, dielectric, and ferroelectric properties of BaxSr(1−x)TiO3 (x = 0.5, 0.6, 0.7) ceramics

Dielectric studies of sintered pellets of barium strontium titanate, BaxSr(1−x)TiO3 (BST) with different compositions (x = 0.5, 0.6, 0.7) were carried out as a function of temperature in the range 35–297 K. The phase transformation temperature of cubic (paraelectric), tetragonal (ferroelectric), rhombohedral (ferroelectric), and orthorhombic (ferroelectric) phases of the BST ceramics with different strontium contents has been determined. The dielectric properties of the BaxSr(1−x)TiO3 pellets have revealed that Curie temperature decreased on replacing Ba by Sr. The Curie temperatures of Ba0.5Sr0.5TiO3, Ba0.6Sr0.4TiO3, and Ba0.7Sr0.3TiO3 were found to be 245 K, 260 K, and 285 K, respectively. Further, cubic, tetragonal, orthorhombic, and rhombohedral phases were observed for the BST pellets with x = 0.5, 0.6, 0.7 in the low temperature range of 35–297 K. The dielectric studies revealed higher dielectric constant and low dielectric loss for Ba0.6Sr0.4TiO3 sample than that of other compositions of the BST. Polarization–electric field (P–E) hysteresis loop measurements for Ba0.6Sr0.4TiO3 ceramic pellet was carried out with different applied electric fields in the range 1.39 to 4.86 kV/cm and in the temperature range of 108–323 K to study the variation in remanent polarization (Pr), saturated polarization (Ps), and coercive field (Ec). The saturated polarization and remanent polarization were found to increase steadily up to the temperature of 165 K and to decrease drastically at about 323 K as a consequence of ferroelectric to paraelectric transition.