Ferroelectric Tetragonal Phase Research Articles

Structural and microstructural description of relaxor-ferroelectric transition in quenched Na1/2Bi1/2TiO3[sbnd]BaTiO3

Quenching lead-free Na1/2Bi1/2TiO3-based ceramics from sintering temperature is established to increase the depolarization temperature, Td and the lattice distortion. In situ synchrotron X-ray diffraction measurements were carried out on furnace cooled and quenched Na1/2Bi1/2TiO3 - BaTiO3 (NBT-BT) with 6 and 9 mol. % BT to discern the field-induced ferroelectric order. Phase fractions were determined from full pattern Rietveld refinements and utilized together with the change in unit cell volume to calculate volumetric strain resulting from phase transformations. NBT-6BT demonstrates a cubic symmetry in the furnace cooled state but quenching stabilizes the rhombohedral R3c phase and delays the formation of a field-induced, long range-ordered tetragonal phase, thereby shifting the onset of macroscopic strain to higher fields. A field-induced phase transition from a weakly distorted rhombohedral to tetragonal phase can be observed in furnace cooled NBT-9BT. However, this phase transition cannot be detected in quenched NBT-9BT, since the ferroelectric tetragonal P4mm phase is stabilized in the initial state. In contrast to the furnace cooled materials, both the quenched compositions exhibit overall negligible volumetric strain as a function of electric field. Furthermore, scanning electron micrographs of chemically etched, poled and unpoled samples reveal an increased lamellar domain contrast in the quenched materials. All these findings strengthen the hypothesis of a stabilized ferroelectric order resulting in the absence of a field-induced phase transformation in quenched NBT-BT.

Order-disorder nature and elastic anomaly of successive phase transition of (K0.5Na0.5)NbO3 proved by broadband Brillouin scattering

ABSTRACT The importance of the environment-friendly lead-free piezoelectric materials has attracted much attention. The (K0.5Na0.5)NbO3 (KNN) crystals with the perovskite structure undergo the cubic (C) to tetragonal (T) ferroelectric phase transition at T CT = 430 °C, and the tetragonal to monoclinic (M) structural phase transition at T TM = 190 °C. The elastic properties and relaxation process of these phase transitions of the KNN crystals have been studied by broadband Brillouin scattering. The softening of the LA and TA velocities was observed in the vicinity of T CT and T TM. The power law behavior of the velocity indicates three-dimensional fluctuations. The broadband central peak showed the critical slowing down in the vicinity of the T CT and T TM. The slowing down is attributed to the order-disorder nature of the off-center displacement of Nb in KNN.

Thickness dependence of phase stability in epitaxial (HfxZr1−x)O2 films

The thickness dependence of the crystal structure in epitaxial $({\mathrm{Hf}}_{x}{\mathrm{Zr}}_{1\ensuremath{-}x}){\mathrm{O}}_{2}$ $(x=0,0.5,1)$ films is demonstrated. X-ray diffraction measurements suggest that the crystal phase changes from the monoclinic to the orthorhombic and tetragonal phases sequentially as film thickness decreases in $\mathrm{Hf}{\mathrm{O}}_{2}$ and $({\mathrm{Hf}}_{0.5}{\mathrm{Zr}}_{0.5}){\mathrm{O}}_{2}$ films. Both films are very thin at the ferroelectric orthorhombic phase $(<5\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$, but the $({\mathrm{Hf}}_{0.5}{\mathrm{Zr}}_{0.5}){\mathrm{O}}_{2}$ films are thicker than the $\mathrm{Hf}{\mathrm{O}}_{2}$ films. In $\mathrm{Zr}{\mathrm{O}}_{2}$ films, the monoclinic phase changes into the tetragonal phase as film thickness decreases. This means that the ferroelectric orthorhombic phase was not observed in the present study. However, ferroelectricity was observed for the present $\mathrm{Zr}{\mathrm{O}}_{2}$ films in the film thickness around the thickness boundary where the tetragonal and monoclinic phases stabilize. We confirmed the field-induced phase transition from the tetragonal to the orthorhombic phase in these $\mathrm{Zr}{\mathrm{O}}_{2}$ films by micro-x-ray diffraction measurement, which suggested that the phase transition takes place due to the small free energy difference between the ferroelectric orthorhombic phase and paraelectric tetragonal phase. Our experimental results agree with theoretical reports of the thickness dependence of the crystal structure in epitaxial films with a surface energy effect.

Physics-based optimization of Landau parameters for ferroelectrics: application to BZT–50BCT

In analogy to thermochemical parameter optimization in the CALculation of PHAse Diagrams (CALPHAD) approach that relies on a wide variety of experimental measurements, a thermodynamic parameter optimization strategy to describe the polarization response with single-crystal Landau coefficients is documented herein to bridge the gap between CALPHAD, Landau theory and the generality of phase field theory. As an example, anisotropic Landau coefficients are obtained by starting from experimental parameters for Pb-free 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–50BCT). Thermodynamic parameters are optimized separately for the rhombohedral (R) and tetragonal (T) ferroelectric phases using a combination of single-crystal and polycrystalline polarization and permittivity data. Parameters are validated against dielectric permittivity as a function of temperature from single-crystal and polycrystalline samples. The optimized parameters correctly predict the sequence of phase transitions as a function of temperature and the paraelectric–ferroelectric transition at 355.5 K is within the experimentally reported range. An upper thermodynamic limit is predicted for R + T metastable coexistence at 302.3 K in agreement with the experimentally measured transition to a stable single T phase for this chemistry at 302 K. The detailed parameter optimization procedure enables the identification of single-crystal tensor properties from experimental measurements for a wide variety of chemistries.

Low-temperature electrical characteristics of nanocrystalline BaTiO3 thin films for cryogenic applications

Ferroelectric thin films are vital in a large number of applications due to their promising properties. Although ferroelectric films' electrical response is studied at high temperatures, their low-temperature behavior is not well understood. In the present study, the εr-V and I-V characteristics of BaTiO3 (BTO) thin films are explored at cryogenic temperatures. BTO thin films have systematically deposited different Ar/O2 ratios by RF sputtering and investigated their structural, microstructural, optical, and electrical properties. The microstructures of these films are well-packed with uniform grain growth and revealed lower rms roughness. The thickness of the films (~170 nm) is obtained by cross-sectional scanning electron microscope images and transmittance spectra. There is not much variation in the optical bandgap, which shows the full stoichiometry and similar thickness of the films. The εr-V response of the film measured at 387 K shows the asymmetry in dielectric constant maxima value. It signifies that there are movable ions and charge accumulation at the interface of film and electrodes. The dielectric response obtained as a temperature function exhibited a Tc of 387 K, indicating the phase transition from ferroelectric tetragonal phase to paraelectric cubic phase. The I-V characteristics of the film measured at 300 K revealed the leakage current of 10−6 Amp, whereas, at 43 K, it is 8.83 × 10−10 Amp. The slope of the I-V curve of the film measured between 1 and 5 V displayed the Ohmic nature. The slope of the film obtained at 6–10 V indicated the space charge limited conduction mechanism, which corresponds to discrete trap carriers. Therefore, trap carriers assisted discrete conduction mechanism is one of the leading factors controlling the conduction process in BTO oxide thin films. The acquired electrical response of the BTO films deposited at 50 Ar is promising for cryogenic devices.

Electric-field response of polar nanodomains in BaTiO3

In this study, we have investigated the electric-field response of polar nanodomains in the ferroelectric tetragonal phase of BaTiO3. Polar nanodomains were observed by a combination of scanning transmission electron microscopy (STEM) and convergent-beam electron diffraction (CBED). By applying an electric-field, significant changes in the distributions of nanometer-size domains were observed, besides the changes in the configurations of mesoscopic 90° and 180° ferroelectric domains. The obtained CBED patterns are categorized into three. One has higher tetragonal symmetry, and the other two show a deviation from tetragonal symmetry and exhibit a left-right reversal relation with each other. We propose a structural model of the rhombohedral nanodomain redistribution to reproduce the observed CBED patterns. The model consists of a balanced change in volume and size of rhombohedral nanodomains.

Design morphotropic phase boundary composition in the Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTio3 system and its performance

ABSTRACT Using composition designing, Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ceramics with compositions around the morphotropic phase boundary (MPB) were prepared by the solid-state reaction method via the columbite and wolframite precursor techniques. X-ray diffraction (XRD) measurement and XRD peaks fitting combined with electrical performance characterization confirm the occurrence of composition-induced ferroelectric phase change, and the sintered PIN-PMN-PT ceramics present the coexistence of rhombohedral and tetragonal ferroelectric phases. Composition exerts great influence on the relative density of the sintered ceramics, and the 0.28Pb(In1/2Nb1/2)O3-0.40Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (0.28PIN-0.40PMN-0.32PT) ceramics exhibit rather uniform microstructural morphology with high relative density of 94.4%. Dielectric, ferroelectric, and piezoelectric performance characterization also confirm the existence of the MPB effects, where the composition having performance maximum presents slight difference, proving that MPB has the composition region. Dielectric response behavior fitting and Raman spectroscopy measurement confirm the PIN-PMN-PT ceramics approach normal ferroelectrics with apparent diffusive transition characteristic and the occurrence of composition-induced ferroelectric phase change.

Origin of magnetic, magnetoelectric effect and the influence of reentrant ferroelectric phase on the structural and multiferroic properties of Dy3+-Fe3+ co-substituted BaTiO3 ceramics

Retain of phase pure ferroelectric tetragonal phase (P4mm) achieved from the coexistence of paraelectric hexagonal phase (P63/mmc) + ferroelectric phase without the loss of polarisation and magnetization under the Dy3+-Fe3+ co-substitution on BaTiO3, Ba1-yDyyTi1-xFexO3 (x = 0.05; y = 0; 0.005; 0.010 and 0.015) ceramics. A small amount of Dy substitution enhances the inhibition of vacancy formation and suppresses the defect concentration through the decrease of the hexagonal phase. The unexpected ferromagnetic nature in the non-magnetic tetragonal phase in y = 0.015 ceramics unambiguously depends on the formation of the paramagnetic defect, Ti3+ for the charge compensation process that induces magnetic moment. The observed ferromagnetic nature in y = 0.01 ceramics originated from the Fe3+-O2−-Fe3+ super-exchange and Dy3+-O2−-Dy3+ interactions which are stronger than the magneto-crystalline anisotropy (y = 0.015). For the first time, multiferroic properties (magnetodielectric and magnetoelectric) were reported in this work. The magnetoelectric coupling effect originated from the co-contribution of magnetocrystalline anisotropy due to spin–orbit interaction through symmetry breaking and microstrain.

Diffuse and relaxor phase transitions of Ba 0.95Bi 0.05Ti 1-xFe xO3 ceramics at x=0.00 to 1.00 of Fe content, prepared by solid state method

The dielectric properties of iron and bismuth co-substituted BaTiO3 ceramic with the formula: Ba 0.95Bi 0.05Ti 1-xFe xO3 (BBTFx) for x=0.00 to 1.00, synthesis with solid state route, were characterized. The results of dielectric permittivity dependence of temperature show three dielectric phase transitions from a rhombohedral ferroelectric to orthorhombic ferroelectric (TR-O) then to a tetragonal ferroelectric phase (at TO-T), and finally to cubic paraelectric at the Curie temperature (Tc). Calculating the relaxation parameters of ΔTrelax and the dispersion factor ΔƐ’r,max/ Ɛ’r,max, we have found that all the ceramics present a relaxation and a dispersion phenomenon. And the phase transition TO-T for x = 0.00 has the highest value of ΔTrelax while the dispersion factor has the highest value for the phase transition Tm at x = 0.60. The diffuseness parameter γ refined from Uchino law showed a diffuse phase transition for all the ceramics. While γ has a value close to 1 for TR-O at x = 0.00, which indicate a standard Curie-Weiss law. The dielectric evolution as function of frequency shows a resonance behavior for x=0.00 of Fe content while for the other ceramics we obtained a classical ferroelectric behavior.

Critical Role of Order-Disorder Behavior in Perovskite Ferroelectric KNbO3.

The evolution of local atomic configuration and macroscopic electrical properties of KNbO3 is investigated in detail using ab initio molecular dynamics simulations within the framework of density functional theory. By analyzing the local off-center displacements of K and Nb atoms, the presence of the crossover of displacive and order-disorder mechanisms in the NbO6 octahedron due to orbital hybridization is found, whereas the K is a completely displacive type due to the nonoriented ionic K-O bond. Besides, the order-disorder behavior of Nb atoms is enhanced with the increase in temperature, especially undergoing the phase transition. The predicted high dielectric constant of KNbO3 confirms the key role of the Nb's order-disorder behavior. We discover that the anomalous increase in dielectric constant in the vicinity of the phase boundary is not only from the transformation of the polarized direction but also from the enhancement of order-disorder contribution in the nonpolarized direction. The high dielectric constant with large spontaneous polarization boosts the piezoelectricity at the orthorhombic-tetragonal phase boundary of 500 K, giving rise to the nearly 100% increase than that of 300 K. A rebonding model is developed to illustrate the origin of high piezoelectricity around the tetragonal ferroelectric phase boundary, and the significance of introducing a tetragonal structure is emphasized for developing high piezoelectricity in the inorganic perovskite ferroelectrics.

Effect of A-site off-stoichiometry on the microstructural, structural, and electromechanical properties of lead-free tetragonal 0.80Na0.5Bi0.5TiO3–0.20BaTiO3 (NBT–20BT) piezoceramic

A-site off-stoichiometry has been an efficient method to enhance the electromechanical properties of lead-free Na0.5Bi0.5TiO3(NBT)-based piezoceramics. In this work, we have reported the effect of Na/Bi off-stoichiometry on the microstructural, structural, and electromechanical properties of the tetragonal 0.80Na0.5Bi0.5TiO3–0.20BaTiO3 (NBT–20BT) ceramic. The maximum piezoresponse ~ 115 pC/N is obtained for 4 mol% Na-deficient (20BT–Na46) and 2 mol% Bi-excess (20BT–Bi52) compositions. It is a 25% increment over the piezoresponse of the stoichiometric composition (20BT–Na50 ~ 90 pC/N). The enhancement in piezoresponse has been attributed to an optimized presence of polar-structural heterogeneity/disorder in the poled ceramic matrix and an optimized distortion of the long-range tetragonal ferroelectric phase. It is established that A-site off-stoichiometry is influencing the polar-structural heterogeneity/disorder and tetragonal lattice distortion via the grain size.

Interface control of tetragonal ferroelectric phase in ultrathin Si-doped HfO2 epitaxial films

Nanoscaled HfO2-based ferroelectric thin films are a favored candidate for the integration of next-generation memory and logic devices. The unique advantage is that the ferroelectric polarization becomes more robust than the traditional perovskite ferroelectrics when the size is reduced. Understanding and controlling the ferroelectricity requires high-quality epitaxial thin films to explore intrinsic ferroelectric mechanism and evaluate device applications. Here, we report a semicoherent growth of ITO as a bottom electrode that enables genuine ultrathin epitaxial films of Si-doped HfO2 on YSZ[001]/[110]/[111] substrates. The deposited films, which are under epitaxial compressive strain, display large ferroelectric polarization values up to 42 μC/cm2 and do not need wake-up cycling. Structural characterization reveals the presence of crystalline domains with short axes of the tetragonal structure oriented perpendicular to the substrate. Using piezoforce microscopy, polar domains can be written and read and can be reversibly switched with a phase change of 180o. Ferroelectric polarization can be controlled by ITO surface polarity which can easily exploit the interfacial valance mismatch to influence the electrostatic potential across the interface. These findings have implications for our understanding of ferroelectric switching and offer easy method to manipulate domain reversal state in HfO2-based ferroelectric materials.

Large electrostrictive coefficient with high electro‐strain dominated by modified ergodic state in BNT‐based solid solutions

AbstractFor ferroelectric electrostrictors, shifting their Curie temperature TC to the ambient temperature is an effective way to enhance their electrostrictive effect. However, the enhanced electrostrictive coefficient Q33 in this way is often accompanied with an inferior electro‐strain. In this work, by introducing CaZrO3/BaZrO3 as the special kind of solid solution, with an effective regulation on the ergodic state, we simultaneously realize a larger room‐temperature electrostrictive coefficient Q33 (~0.04337 m4/C2) with a superior electro‐strain (~0.41%) in Bi0.5Na0.5TiO3‐based relaxor ferroelectric ceramics. The ions substitution with larger radius in either A‐site or B‐site of perovskite structure tends to facilitate the evolution from ferroelectric tetragonal phase P4mm to relaxor tetragonal phase P4bm along with the decrease in polarity in crystal, thereby shifting the transition temperature TF‐R below room temperature. As a result of the effective regulation on the ergodic state, a large electro‐strain with low hysteresis, just like electrostrictors, is successfully realized in BNT‐based ferroelectric ceramics. Our investigation provides an effective way to simultaneously enhance the electrostrictive coefficient Q33 and electro‐strain for practical applications in precisely controlled displacement.

Phase Formation, Structure, and Dielectric Properties of Modified Potassium Sodium Niobate Ceramics

We have prepared (1 – x)(K0.5Na0.5)NbO3–xCa(Cu1/3Nb2/3)O3 (x = 0–0.1, ∆х = 0.02) ceramics by solid-state reactions and studied their phase formation, structure, and dielectric and ferroelectric properties. The formation of a phase with the perovskite structure and an orthorhombic unit cell has been demonstrated in all of the samples. Ferroelectric phase transitions have been confirmed by dielectric spectroscopy and laser second harmonic generation measurements. The temperatures of the phase transitions from the orthorhombic ferroelectric phase to the tetragonal ferroelectric phase and to the cubic (paraelectric) phase have been shown to decrease with increasing x. We have analyzed the composition dependences of dielectric parameters in the system studied.

Modulation in polymer properties in PVDF/BCZT composites with ceramic content and their energy density capabilities

AbstractThe lead‐free 0.5((Ba0.7Ca0.3)TiO3)‐0.5(Ba(Zr0.2Ti0.8))O3(BCZT) piezoceramics were synthesized using sol‐gel method. The Rietveld analysis of X‐ray diffraction (XRD) data and differential scanning calorimetry (DSC) studies of as‐synthesized BCZT powder suggests the co‐existence of ferroelectric orthorhombic (O) and tetragonal (T) phases at room temperature (RT). The value of curie temperature (TT‐C) as depicted from DSC and dielectric studies was found to be ≈ 110°C. The BCZT ceramic particles were dispersed in the polyvinylidene fluoride (PVDF) matrix, an electroactive polymer with great ferro/piezoelectric response in its distinct β and γ phases, to form ferroelectric ceramic‐polymer composites for their applications in flexible energy storage capacitors. The present work reports the Fourier‐transform infrared spectroscopy (FTIR), XRD, dielectric, ferroelectric, and energy density properties of PVDF/BCZT composite films having different wt% of BCZT content fabricated by the solution‐cast technique. The FTIR and XRD studies depict the γ‐PVDF and pure BCZT phases in composite films. The dielectric studies estimated the relative permittivity (εr) of a composite film with 50 wt% of BCZT content to be ≈ 31 (at 120 Hz) which was about three times as compared with that of pure PVDF. The dielectric loss (tan δ) was maximum ≈ 0.15 (at 120 Hz) for 50 wt% BCZT composition. The ferroelectric studies and energy storage calculations showed that the value of remnant polarization (Pr), coercive field (Ec) and energy storage density (W) attain the maximum value of 0.63 μC/cm2, 21.20 kV/cm, and 70.46 mJ/cm3, respectively for the film sample having 40 wt% BCZT content. The maximum energy storage efficiency, η (%) is calculated to be ≈ 60 for 50 wt% BCZT composition. The results indicated that the incorporation of BCZT particles in the PVDF matrix improved the overall polarization (polar and interfacial) which enhance the electric properties of composite films. The ferroelectric studies with temperature revealed the PVDF/BCZT composition‐dependent polymer or ceramic dominance in the behavior of composite films. With the maximum value of relative permittivity (εr) and energy storage efficiency (η), the PVDF/BCZT composition with 50 wt% of BCZT content has been optimized for applications in flexible energy storage capacitors.

Dielectric and Thermal Properties of Tetragonal PbTiO3 Nanoparticles/Clusters Embedded in Lithium Tetraborate Glass Matrix

PbTiO3 nanoparticles/clusters embedded in lithium tetraborate glass matrix (glass nanocomposite (GNCs)) of composition (100-x) Li2B4O7-xPbTiO3 (where x = 5, 10, 15 and 20 in mol %) were synthesized. The presence of glassy phase in all GNCs samples was identified by X-ray diffraction (XRD) and differential scanning calorimetric (DSC) studies. The structure of PbTiO3 used in the preparation of these samples is a ferroelectric tetragonal phase (space group P4mm) which is confirmed by Rietveld refinement of XRD data. Transmission electron microscopic (TEM) images exhibit PbTiO3 nanoparticles/clusters phase embedded in lithium tetraborate glass matrix. The ferroelectric to paraelectric phase transition of PbTiO3 nanoparticles/clusters in the GNCs samples was established from DSC and dielectric studies. The thermal, density, dielectric and Ac conductivity behavior of the GNCs samples depends on the change in the coordination number of the network former and the concentration of PbTiO3 in the glass matrix.

Large electrostrictive effect and strong photoluminescence properties in Sm2O3-modified lead-free potassium sodium niobate-based piezoelectric ceramics

In this work, the phase transition behavior and electrostrictive and photoluminescence properties of Sm2O3-modified 0.965(K0.48Na0.52)(Nb0.95Sb0.05)–0.035Bi0.5(Na0.82K0.18)0.5HfO3 (KNNS–0.035BNKH) ceramics were investigated. Results showed that the phase structure of the Sm2O3-modified ceramics evolved from coexisting orthogonal and tetragonal ferroelectric phases to a relaxor pseudocubic phase along with the strong destruction of the long-range ferroelectric order. Domain switching in Sm-modified ceramics with a relaxor pseudocubic phase became difficult, evident from the PFM images. Consequently, large electrostrictive effect with an electrostrictive coefficient of 0.022 m4/C2 was obtained in 1.0 mol% Sm-modified samples. With regard to long-term stability, the materials exhibited temperature-independent (20–100 °C) and fatigue−free (up to 105 cycles) behavior, which guarantees their application in various devices. The KNNS–0.035BNKH–xSm ceramics have the advantages of photoluminescence performance with bright orange emission under 407 nm visible light excitation. Overall, KNNS−0.035BNKH−xSm ceramics have broad application prospects in multifunction devices due to their large electrostrictive effect, excellent photoluminescence performance, and long-term stability.

Improved pyroelectric properties and domain structures via poling and depoling effects in Mn-doped PIN–PMN–PT single crystals

The poling and depoling effects were investigated on the pyroelectric performance and the domain structures of Mn-doped PIN–PMN–PT (the abbreviation of the 0.15Pb(In1/2Nb1/2)–0.55Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 crystals doped with 1% manganese, nominal composition) single crystals to optimize the poling process. With the poling field up to 3Ec, the crystals can reach the best pyroelectric properties and the characteristic parameters are optimized as p = 9.39 × 10–4 Cm−2 K−1 and Fd = 25.7 × 10–5 Pa−1/2. The single domain state cannot be achieved with further increasing the electric field due to the pinned effect induced by the $$({\text{Mn}}^{{2 + }} )_{Ti}^{{{\prime \prime }}} - {\text{V}}_{O}^{{{ \cdot \cdot }}}$$ dipoles and the internal stress field. Due to the enhanced thermal stability, the crystals increase the working temperature compared to the undoped PMN-PT crystals, reaching 100 °C, that is suitable for applications as the infrared devices. When the temperature is above 100 °C, the pyroelectric performance will deteriorate seriously due to the successive phase transitions from the rhombohedral ferroelectric phase to the tetragonal ferroelectric phase at TR–T, and to the cubic paraelectric phase at TC/Tm.

Engineering room-temperature multiferroicity in Bi and Fe codoped BaTiO3

Fe doping into BaTiO3 stabilizes the paraelectric hexagonal phase in place of the ferroelectric tetragonal one. We show that simultaneous doping of Bi along with Fe into BaTiO3 effectively enhances the magnetoelectric (ME) multiferroic response (both ferromagnetism and ferroelectricity) at room temperature, through careful tuning of Fe valency along with the controlled recovery of the ferroelectric-tetragonal phase. We also report a systematic increase in large dielectric constant values as well as reduction in loss tangent values with relatively moderate temperature variation of the dielectric constant around room temperature with increasing Bi doping content in Ba1−xBixTi0.90Fe0.10O3 (0 ≤ x ≤ 0.10), which makes the higher Bi–Fe codoped sample (x = 0.08) promising for use as a room-temperature high-κ dielectric material. Interestingly, the x = 0.08 (Bi–Fe codoped) sample is not only found to be ferroelectrically (∼20 times) and ferromagnetically (∼6 times) stronger than x = 0 (only Fe-doped) at room temperature, but also observed to be better insulating (larger bandgap) with indirect signatures of larger ME coupling as indicated from anomalous reduction of the magnetic coercive field with decreasing temperature. Thus, room-temperature ME multiferroicity has been engineered in Bi and Fe codoped BTO (BaTiO3) compounds.

Unraveling the electronic, optical, ferroelectric, and electrocaloric properties of [formula omitted] thin film: Insight from first-principles effective Hamiltonian

In this work, electronic, optical, dielectric and ferroelectric properties of PbxSr1-xTiO3 (PST) thin film are systematically investigated. This system is studied from first-principles computations using density functional theory (DFT) and effective Hamiltonian. In this regard, the influence of Pb doping on the above properties is elucidated to unravel a global description of this material. From the calculations along the higher symmetry direction, and upon substitution of Sr content, a direct band gap is obtained. Concerning the optical properties, the curves of refractive index revealed a systematic variation with composition. The results were compared with other reviews and showed a good agreement. Through a detailed analysis, investigations of several parameters are reported. However, an appropriate level of Pb doping can provide tremendous informations about this material, representing an important step toward deeper understanding for furthering knowledge, which may open the door for practical applications. This work reveals the contribution of Pb content especially on the phase transitions. The increase in the concentration of Pb shifts the critical temperature towards higher temperature and evolves the dipoles to switch for a large temperature range, resulting a large tetragonal (ferroelectric) phase and anomalous volume expansion, which in turn could improve the ferroelectric transition temperature. The dielectric constant, polarization and pyroelectric coefficient are examined as a function of the temperature. A typical hysteresis loops were clearly observed to confirm the ferroelectric-paraelectric phase transition. Besides, the electrocaloric effect (ECE) of PST thin film is also predicted with particular attention to the applied electric field and concentration x. Our calculations also revealed that PbxSr1-xTiO3 thin film exhibits a large room-temperature adiabatic temperature change (ΔT), which largely depends on the Pb content. The increase of Pb composition improves the adiabatic temperature change and enlarges its maximum at a relatively higher temperature. An enhancement regarding the ECE may potentially open the door for practical cooling device applications.