Decrease Of Remnant Polarization Research Articles

Understanding the depolarization phenomena in (1−x) Na0.5Bi0.5TiO3. (x) Ba0.85Ca0.15Ti0.90Zr0.10O3 solid solutions using in-situ temperature dependent Raman spectroscopy

A decrease in depolarization temperature (T d) from 456 K to 352 K was observed with an increase in BCZT substitution in the NBT for the (1−x) Na0.5Bi0.5TiO3. (x) Ba0.85Ca0.15Ti0.90Zr0.10O3 solid solutions. A transition towards a higher ergodic state was elucidated with an increase in BCZT content that helped to reduce the free energy barrier, hence lesser thermal energy was required to depolarize the modified systems. Furthermore, a decrease in remnant polarization and coercive field, coupled with an increase in energy storage (W stored) and efficiency (η%) with higher BCZT content. In-situ temperature-dependent Raman spectra provide additional insights, highlighting the faster changes in phonon shifts and lifetimes corresponding to the A–O, B–O, and BO6 vibrations around the depolarization temperature (T d). The observed phase transformation to a P4bm phase at temperatures significantly higher than T d is substantiated by Raman shift and phonon lifetime variations in the modes associated with the A–O and B–O vibrations. The transitions can be understood as: at T ∼ T d the polar nano regions (PNRs) start to appear due to weakening of bonds, T > T d all the long-range ferroelectric domains transform to PNRs converting the material to a fully ergodic state, and at much higher temperatures (T ≫ T d) the R3c PNRs vanish and P4bm PNRs appear.

Study structural, dielectric and ferroelectric properties of Pb (Zr1-x Tix)O3 ceramics near the morphotropic phase boundary

In the present work, Pb(Zr(1-x)Tix) ceramics (x = 0.50, 0.48, 0.45 and 0.42) were prepared using the solid state reaction method, at the sintaring temperature (1100 oC ) for (6hr).X-ray diffraction results demonstrate that all the samples lie within the morphtropic phase boundary (MPB) region in the pure perovskite tetragonal structure with Miller transactions (100), (110), (111), (200), (210), (211), (220), (103) and (311) that the prevailing trend is (110) and the results of plasticity microwave very close sense of distance intra-convergent also relatively few crystalline defects. Increasing the bulk density of the true density of altered concentration of zirconium and titanium. Results of the examination microscope also showed that the particle size (Dnm) be tight between the samples and the homogeneity of the granules, as well as increasing the homogeneity of compositional structure, causing an improvement in the structural and electrical properties. Shown technique results EDAX compound of the interacting elements of the composition and there is little difference between the real weight and the weight is noticeable. The temperature and concentration of titanium dependences of the dielectric constant of the ceramics has been investigated in detail. Excellent dielectric properties have been obtained for the selected compositions. Polarization-Elctric field hysteresis studies were carried out for all compositions at room temperature. It was found that with the increase of concentration of titanium content in the composition the remnant polarization decreases and ferroelectric loops get constricted.

Enhanced energy storage density with excellent temperature-stable dielectric properties of (1-x)[(Bi0.5Na0.5)0.94Ba0.06TiO3]-xAgNbO3 lead-free ceramics

Lead-free (1-x)[(Bi0.5Na0.5)0.94Ba0.06TiO3]-xAgNbO3 (abbreviated as BNTBT-100xAN) ceramics were fabricated using a conventional solid-phase reaction technique. The effect of the antiferroelectric AgNbO3 dopants for fatigue resistance, energy-storage density, temperature-stable permittivity, and conductivity mechanism was systematically investigated. The addition of AgNbO3 led to the decrease of remnant polarization and the increase of dielectric breakdown strength, a large effective energy-storage density of ~1.27 J/cm3 corresponding to the conversion efficiency of ~ 77.5% for BNTBT-5AN ceramic were attained under applied 105 kV/cm field. Meanwhile, it exhibited an outstanding fatigue-resistant performance at 70 kV/cm fixed field up to 105 cycles accompanied with excellent temperature-stable properties in the temperature range of 30 °C ~ 120 °C. Besides, BNTBT-5AN sample has also obtained outstanding temperature-stable permittivity, which was associated with the enhancement of the ergodic relaxor domain structure. A little variance of dielectric content (Δε'/ε'150 °C ≤ ± 15%) was acquired from 40 °C to 387 °C with a small tangent loss (tanδ ≤ 0.05) between 50 °C and 461 °C. Hence, it revealed that the high energy storage properties and excellent dielectric temperature stability for BNTBT-5AN ceramic were conducive to its better applications in electronic equipment.

Effect of Gamma Irradiation on the Structural, Optical, Electrical, and Ferroelectric Characterizations of Bismuth-Modified Barium Titanate Ceramics.

Materials with ferroelectric properties, low bandgap energies, high polarization, low loss, and thermal stability are essential for future solar-cell applications. Researchers have attempted to obtain such materials by using several approaches. In this vein, a novel approach is reported in this work using gamma ray irradiation. The effect of gamma radiation on the structural, optical, and ferroelectric characterizations of bismuth (Bi)-doped barium titanate (BaTiO3 (BT)), namely Ba0.95Bi0.05TiO3 ceramics (abbreviated as (Bi:BT)), was investigated. X-ray diffraction, structure refinement, and Raman study revealed the presence of a perovskite structure with a tetragonal phase in all investigated samples. Morphological study revealed a nonuniform grain size and some porosity. Gamma irradiation-induced combined effects were proved by a detailed analysis of bond lengths, bond angles, octahedral distortions, oxygen vacancies, and charge compensations. Electron paramagnetic resonance (EPR) study gave direct evidence of oxygen vacancies in the irradiated samples. After gamma irradiation, UV–vis study indicated a decrease in the bandgap from 3.14 to 2.80 eV and a significant increase in visible light absorption. Cole–Cole plots confirm as an increase in gamma-ray dose results in higher levels of electron hopping. Study of the P–E hysteresis loop demonstrated that ferroelectric properties could be maintained after gamma irradiation, with a slight decrease in remnant polarization. The behaviour of the P–E was correlated with increasing gamma dose in the investigated ceramics, demonstrating a strong gamma dependence in the loops’ profile. We guess that the present approach may be a promising technique for enhancing the multifunctionality of electronic devices.

Achieving Enhanced Energy‐Storage Performances in Bi0.5(K0.15Na0.85)0.5TiO3 Ceramics Modified by Sr(Ti0.85Zr0.15)O3

Lead‐free (1−x)Bi0.5(K0.15Na0.85)0.5TiO3‐xSr(Ti0.85Zr0.15)O3 ((1−x)BKNT‐xSTZ, x = 0.1–0.4) ceramics are synthesized by citrate combustion method. The grain size is reduced, and the high‐temperature shoulder dielectric peak (Tm) shifts toward low temperature, while the low‐temperature shoulder dielectric peak (Ts) shifts toward high temperature as x increases. The remnant polarization decreases and slimmer hysteresis loops are realized with x increasing. The optimal energy density (Wre ≈2.85 J cm−3) with high efficiency (η ≈ 81%) is obtained for 0.7BKNT‐0.3STZ at 160 kV cm−1. More importantly, excellent frequency stability and enhanced temperature‐dependent energy properties (Wre ≈ 1.12 J cm−3 and η ≈ 94%) of 0.7BKNT‐0.3STZ ceramic are obtained at 100 kV cm−1 and 120 °C.

Dielectric, ferroelectric, and energy storage properties of Ba(Zn1/3Nb2/3)O3-modfied BiFeO3–BaTiO3 Pb-Free relaxor ferroelectric ceramics

Pb-free bulk ceramics (1-x)[0.65BiFeO3-0.35BaTiO3]-xBa(Zn1/3Nb2/3)O3 were produced by traditional solid-state reaction route. In this experiment, Ba(Zn1/3Nb2/3)O3 (BZN) was introduced to destroy long-range order domains in order to obtain higher energy storage performance. Impedance and XPS analysis indicate that oxygen vacancies exist and participate in relaxation processes at high temperatures. With the increase of BZN content, the dielectric relaxation behavior is improved, the hysteresis loop becomes thinner, remnant polarization decreases, and the breakdown electric field increases to 180 kV/cm in 15BZN. A maximum Wrec (1.62 J/cm3) is eventually reached in 7BZN with great temperature stability. The highest efficiency is 91% in 15BZN with Wrec of 1.28 J/cm3. Charge-discharge tests show that ceramics have a quick discharge time of t0.9 < 0.1 μs, which makes BZN-doped ceramics a potential candidate for energy storage devices.

A Study on the Temperature-Dependent Operation of Fluorite-Structure-Based Ferroelectric HfO2 Memory FeFET: A Temperature-Modulated Operation

We report on the temperature-dependent operation of fluorite-structure-based ferroelectric FET (FeFET) emerging memory. A temperature range (− 40 °C to 40 °C) is used to explore the FeFET characteristic relation to operating temperature. The memory window (MW) shows a modulated response that features a reciprocal MW dependence on temperature, such that a maximum of the MW is realized at − 40 °C. The gradual MW closure upon temperature increase is attributed to the ferroelectric (FE) polarization change with temperature. On the contrary, the FE coercive field shows a minor variation with operating temperature. The FeFET state readout shows a trend of ${V}_{\text {th}}$ shift with temperature such that the decrease in remnant polarization, as well as the substrate effects, causes a maximized shift for erase (ER) state compared to the program (PG) one. The benchmark of Si-doped hafnium oxide (HSO) and hafnium zirconium oxide (HZO) shows comparable trends for dependence on temperature. The temperature cycling by repetitive sweep from − 40 °C to 40 °C shows reproducible MW and PG/ER readout trends with a predictable FeFET response over temperature. This suggests system design techniques for mitigating the variation effects. The FeFET characteristics are explored with insight on physical mechanisms and FE response to temperature variation.

A Study on the Temperature-Dependent Operation of Fluorite-Structure-Based Ferroelectric HfO2 Memory FeFET: Pyroelectricity and Reliability

We report on the high-temperature operation and reliability of the Si-doped hafnium oxide (HSO) ferroelectric FET (FeFET) emerging memory. In this study, we explore the role of high-temperature operation of the ferroelectric (FE) material on the FeFET in the temperature range of 40-120 °C. The inverse memory window (MW) dependence on temperature leads to a very small MW size (~300 mV) at 120 °C. The recovery of MW size at room temperature (RT) indicates a potential pyroelectric effect as a cause for MW closure upon high-temperature operation. The FeFET state readout shows pronounced effects to erase (ER) threshold voltage (Vth) shift, due to the decrease in remnant polarization and improved substrate Vth shift as the temperature increases. The endurance reliability measured for temperature range (-40 °C to 40 °C) with 105 cycles shows a maximized initial MW at low temperatures, whereas higher postcycling interface trap generation occurs as the temperature increases. The FeFET 10 h retention tests at 0 °C and 40 °C were extrapolated to ten years and indicated stable properties independent of temperature. The depolarization field (Ed) dependence on the FeFET stack parameters is studied based on an analytical formula. The Ed decreases with increased permittivity of the FE, interface layer (IL), and increased FE film thickness. Substrate doping and temperature seem to have a small impact on E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> , whereas the FE-IL area ratio tuning below unity lowers the E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> . The role of pyroelectric effect on the FeFET memory and operating temperature-induced endurance and retention reliability concerns are discussed.

Temperature and Frequency Dependent Multiferroic Features of Gadolinium Doped BiFeO3-PbTiO3 Electronic System

Multiferroic gadolinium (Gd) doped BiFeO3 (BFO) and PbTiO3 (PT) samples [(Pb1−xBi0.5xGd0.5x)(FexTi1−x)O3] with x = 0.1, 0.3, 0.5 and 0.7 are formulated by adopting the solid state reaction process. The impact of gadolinium substitution in the crystal structure, morphological behavior and electrical properties has been studied. By altering the Gd concentration in the solid solution a change in the structure is observed that is from tetragonal to rhombohedral. The size of the grain in the compounds reduces as a result of enrich in gadolinium content of the furnished sample. The subsidence of lead minimizes the toxic behavior of the material with significant improvements in dielectric response of gadolinium modified BiFeO3–PbTiO3 synthesized system. From the impedance study, the material presents negative temperature coefficient of resistance characteristics and the impedance is due to the presence of grain and grain boundary effect inside the materials. It is realized that the remnant polarization decreases and frequency dependent ac conductivity increases with the concentration of gadolinium in the electronic system. From conductivity study, the equipped electronic materials show non-exponential type of conductivity relaxation.

Phase field simulation of misfit strain manipulating domain structure and ferroelectric properties in PbZr&lt;sub&gt;(1–&lt;i&gt;x&lt;/i&gt;)&lt;/sub&gt;Ti&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;O&lt;sub&gt;3&lt;/sub&gt; thin films

Ferroelectric domain structures and ferroelectric properties in the hetero-epitaxially constrained ferroelectric thin films can be manipulated by substrate misfit strain. In this work, three kinds of phase structures of PbZr&lt;sub&gt;(1–&lt;i&gt;x&lt;/i&gt;)&lt;/sub&gt;Ti&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;O&lt;sub&gt;3&lt;/sub&gt; thin films, including tetragonal, tetragonal- rhombohedral-mixed and rhombohedral phases, are investigated. Firstly, the ferroelectric domain structures at different substrate misfit biaxial strains are obtained by the phase-field simulation. Then we calculate the polarization-electric field hysteresis loops at different misfit strains, and obtain the coercive field, saturation polarization, and remnant polarization. In the tetragonal PbZr&lt;sub&gt;(1–&lt;i&gt;x&lt;/i&gt;)&lt;/sub&gt;Ti&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;O&lt;sub&gt;3&lt;/sub&gt; (&lt;i&gt;x&lt;/i&gt; = 0.8) thin film, compressive strain contributes to the formation of out-of-plane c1/c2 domain, and tensile strain favors in-plane a1/a2 domain formation. With the increase of compressive strain, the tetragonal phase and the rhombohedral phase coexist in PbZr&lt;sub&gt;(1–&lt;i&gt;x&lt;/i&gt;)&lt;/sub&gt;Ti&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;O&lt;sub&gt;3&lt;/sub&gt; (&lt;i&gt;x&lt;/i&gt; = 0.48) film near the morphotropic phase boundary, while the tensile strain reduces the rhombohedral domain size. In the rhombohedral PbZr&lt;sub&gt;(1–&lt;i&gt;x&lt;/i&gt;)&lt;/sub&gt;Ti&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;O&lt;sub&gt;3&lt;/sub&gt; (&lt;i&gt;x&lt;/i&gt; = 0.2) film, the rhombohedral domains are steady states under compressive strain and tensile strain. As the misfit strain changes from –1.0% to 1.0%, the value of the coercive field, saturation polarization and remnant polarization decrease. Among them, for tetragonal-rhombohedral mixed phase, the reductions of saturation field and remnant polarization are larger than for tetragonal phase and rhombohedral phase. The coercive field of mixed phase decreases rapidly under the compressive strain, but deceases slowly under the tensile strain. It is worth noting that the remnant polarization decreases faster than the saturation polarization in three components of ferroelectric thin film. Due to the electromechanical coupling, when &lt;i&gt;x&lt;/i&gt; = 0.48 at the morphotropic phase boundary it is shown that the remnant polarization reduction is faster than those of the other two types of ferroelectric thin films, and the small coercive field is obtained in the case of large tensile strain. Therefore, tensile strain can effectively improve the energy storage efficiency in ferroelectric thin films, and the efficiency of &lt;i&gt;x&lt;/i&gt; = 0.48 thin film increases significantly compared with that of &lt;i&gt;x&lt;/i&gt; = 0.8 or 0.2 thin film. Both the ratio of rhombohedral/tetragonal phase and the domain size will play a significant role in ferroelectric performance. Therefore, our results contribute to the understanding of the electromechanical coupling mechanism of PbZr&lt;sub&gt;(1–&lt;i&gt;x&lt;/i&gt;)&lt;/sub&gt;Ti&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;O&lt;sub&gt;3&lt;/sub&gt;, and provide guidance for the experimental design of ferroelectric functional thin film materials.

Effects of disorder activated scattering and defect-induced phase on the ferroelectric properties of BaSnxTi1-xO3 (0≤x≤0.28) ceramics

BaSnxTi1-xO3 solid solutions with varying Sn content (x = 0.0–0.28) have been characterized for their structural, dielectric and ferroelectric properties. Rietveld analysis of high resolution X-ray diffraction (HRXRD) data reveals the coexistence of (tetragonal+orthorhombic) phases for x = 0.05, and (rhombohedral+cubic) phases for x = 0.12, and a single phase for the remaining compositions. Raman spectroscopy at room temperature reveals composition induced structural changes, and exhibits disorder-activated scattering at ∼110 cm−1 due to coexisting SnO6 and TiO6 octahedra in BaSnxTi1-xO3 compositions with Sn content x ≥ 0.1. Presence of SnO6 is confirmed both by Raman and infrared (IR) absorption spectroscopy. Incipient growth of a defect-induced semiconducting phase (BaSnO3) builds-up with increasing Sn content (x ≥ 0.05), but remains undetected by X-ray diffraction. It is prominently revealed by the high frequency Raman mode at ∼752 cm−1, which upon de-convolution shows the involvement of two overlapped modes. A decreasing intensity ratio of the two modes with increasing Sn content (x = 0.05–0.15) correlates with the observed decrease in remnant polarization, and a complete overlapping of the modes at a higher level of Sn content (x = 0.27) signifies the onset of relaxor behavior in the dielectric characteristics.

Crystal structural evolution and hybrid improper ferroelectricity in Ruddlesden-Popper Ca3-xSrxTi2O7 ceramics

Hybrid improper ferroelectricity (HIF) has been proposed as a candidate approach to create room-temperature multiferroic materials with an intrinsic electric-field controlled magnetism effect, and HIFs in bi-layered Ruddlesden-Popper Ca3-xSrxTi2O7 ceramics have been confirmed in the present work. The ferroelectric hysteresis loops are observed in these ceramics at room temperature, and the polar orthorhombic structures with oxygen octahedral rotation and tilt modes have been confirmed by room-temperature X-ray powder diffraction. The amplitudes of oxygen octahedral rotation and tilt modes decrease with the increasing x value, which in turn leads to the decrease of remnant polarization in these ceramics. A first-order phase transition has been evidenced by the differential scanning calorimetry measurement, and the temperature of phase transition decreases linearly with the increasing content of strontium cations. It is found that the amplitude of oxygen octahedral distortion is the dominating factor that affects ferroelectric polarization in partial-ordered bi-layered Ca3Ti2O7-based ceramics.

Giant electromechanical strain response in lead‐free SrTiO3‐doped (Bi0.5Na0.5TiO3–BaTiO3)–LiNbO3 piezoelectric ceramics

AbstractLead‐free 0.985[(0.94−x)Bi0.5Na0.5TiO3–0.06BaTiO3–xSrTiO3]–0.015LiNbO3 [(BNT–BT–xST)–LN, x=0‐0.05] piezoelectric ceramics were prepared using a conventional solid‐state reaction method. It was found that the long‐range ferroelectric order in the unmodified (BNT–BT)–LN ceramic was disrupted and transformed into the ergodic relaxor phase with the ST substitution, which was well demonstrated by the dramatic decrease in remnant polarization (Pr), coercive field (Ec), negative strain (Sneg) and piezoelectric coefficient (d33). However, the degradation of the ferroelectric and piezoelectric properties was accompanied by a significant increase in the usable strain response. The critical composition (BNT–BT–0.03ST)–LN exhibited a maximum unipolar strain of ~0.44% and corresponding normalized strain, Smax/Emax of ~880 pm/V under a moderate field of 50 kV/cm at room temperature. This giant strain was associated with the coexistence of the ferroelectric and ergodic relaxor phases, which should be mainly attributed to the reversible electric‐field‐induced transition between the ergodic relaxor and ferroelectric phases. Furthermore, the large field‐induced strain showed relatively good temperature stability; the Smax/Emax was as high as ~490 pm/V even at 120°C. These findings indicated that the (BNT–BT–xST)–LN system would be a suitable environmental‐friendly candidate for actuator applications.

Effect of hysteresis of dipole on remnant polarization in ferroelectrics

Decrease in remnant polarization at lower temperature, or low temperature degradation of polarization, in some ferroelectrics has attracted much attention. To investigate the mechanism of the decrease, phenomenological theory of ferroelectrics and the relevant mechanism of dipole in alternating electric field are used to develop a model of hysteresis-frozen effect of dipole in electric hysteresis loop measurement. Within the frame of Landau-Ginzburg-Devonshire theory, Ising model is used to derive the relationship among remnant polarization, coercive field, and saturated polarization strength. Then, two aspects are investigated: response of a dipole and thermodynamic properties of ferroelectric. Response of a dipole in an electric field is often described by relaxation time, on the assumption that Debye equation is satisfied. Potential barrier in the Debye equation is the Gibbs free energy barrier from one ferroelectric state, +P, to another ferroelectric state, -P. Increase in the Gibbs free energy barrier with temperature decreasing will prolong the relaxation time. As ferroelectrics can be taken as a capacitor, first order response function is used to introduce a hysteresis factor with measuring frequency and relaxation time into the expression of remnant polarization. In the aspect of thermodynamic properties of ferroelectric, the variation of compositions is a significant reason. In numerical simulation based on the derived formula the remnant polarization exhibits a frequency related peak, and shift of the peak depends on some other reasons: the increase of soft-mode coefficient in phase transition shifts the peak towards high temperature; the increases of coercive field, temperature-polarization coefficient (a concept defined in the present paper to indicate increase in polarization with increasing temperature) and saturated electric field shift the peak toward low temperature. Compared with the reported experimental results of BaTiO3/BiScO3 compound ceramics, the results show a good coincidence with numerical simulations. The parameter values of numerical simulation indicate that a large shift toward high temperature in peak of remnant polarization with increasing BiScO3 composition ratio is due to the increase in soft-mode coefficient with only small decrease in the Curie temperature. The soft-mode coefficient and temperature-polarization coefficient are closely related to polarization characteristic, ferroelectric, dielectric and mechanical properties. Therefore, the decrease in remnant polarization at low temperatures, ascribed to the hysteresis of dipole to a constant measuring frequency, may have an influence on changes in various properties, but freezing effect of dipole at low temperature can help ferroelectrics to save data longer.

Effect of Tb substitution on structural, optical, electrical and magnetic properties of BiFeO3

Tb substituted BiFeO3 [Bi1−xTbxFeO3 (x = 0.05, 0.10, 0.15)] have been synthesized by a low temperature assisted Co-precipitation method. Rietveld-refinement of the X-ray diffraction data reveals a transition from rhombohedral (R3c) to orthorhombic (Pnma) phase, i.e. polar to non-polar phase with Tb substitution. The crystallite sizes of Bi1−xTbxFeO3 (x = 0.05, 0.1 and 0.15) are found to be approximately 30, 21 and 15 nm calculated using Debye–Scherrer equation. From transmission electron microscopy analysis, the particle sizes are found to be between 35–40, 30–35, and 25–30 nm, respectively for Bi1−xTbxFeO3 (x = 0.05, 0.10 and 0.15) samples. UV–Vis diffuse reflectance spectra show a decrease of band gap with increase in Tb concentration. 4A1 and 7E Raman modes have been observed in the range 100–650 cm−1 and two phonon modes centred around 1150–1450 cm−1 have also been observed. The changes in Raman modes such as prominent frequency shift, line broadening and intensity reveals the existence of substitution induced structural changes as supported by the Rietveld refinement. Temperature dependent dielectric measurements on the samples show magnetoelectric coupling in terms of a dielectric anomaly near the Neel temperature (TN). An enhancement of magnetization with increasing Tb concentration in BFO has been observed from room temperature magnetization studies. The leakage current density is found to be reduced with the increase of Tb concentration. Further, P–E hysteresis loop studies show a decrease of remnant polarization (Pr) with the increase in Tb concentration predicting a transition from ferroelectric (polar) to paraelectric (non-polar) phase as inferred from X-ray diffraction analysis.

The structural and in-plane dielectric/ferroelectric properties of the epitaxial (Ba, Sr)(Zr, Ti)O3 thin films

Epitaxial (Ba1-xSrx)(Zr0.1Ti0.9)O3 (BSZT, x = 0 – 0.45) thin films were deposited on (LaAlO3)0.3(Sr2AlTaO6)0.35 (LSAT) substrates by pulsed laser deposition. The experimental results demonstrate that the structural, dielectric, and ferroelectric properties of the BSZT thin films were greatly dependent on the strontium content. The BSZT thin films transformed from tetragonal to cubic phase when x ≥ 0.35 at room temperature. The Curie temperature and room-temperature remnant polarization decrease with increasing strontium concentration. The optimal dielectric properties were found in (Ba0.55Sr0.45)(Zr0.1Ti0.9)O3 thin films which is in paraelectric state, having tunability of 47% and loss tangent of 0.0338 under an electric field of 20 MV/m at 1 MHz. This suggests that BSZT thin film is a promising candidate for tunable microwave device applications.

Effect of Dy-substitution on the structural, vibrational, and multiferroic properties of BiFeO3 nanoparticles

Dysprosium (Dy) modified BiFeO3 [Bi1−xDyxFeO3 (x = 0.05, 0.10, and 0.15)] nanoparticles have been synthesized by a low temperature co-precipitation method. Rietveld analysis of X-ray diffraction data reveals a transformation from rhombohedral structure to orthorhombic structure with increase in the Dy concentration. From the transmission electron microscopy analysis, it is observed that the particle sizes of Bi1−xDyxFeO3 (x = 0.05, 0.10, and 0.15) nanoparticles range between 50–70, 40–50, and 30–50 nm, respectively. Raman spectra of Bi1−xDyxFeO3 (x = 0.05) belonging to rhombohedral (R3c) structure show 4A1 and 7E fundamental Raman modes in the range of 100–650 cm−1 and two-phonon scattering modes such as 2A4 (longitudinal optical), 2E8 (transverse optical (TO)), and 2E9 (TO) in the range of 950–1270 cm−1. Suppression, broadening, and shifting of Raman modes have been observed with further increase in Dy concentration. The fundamental Raman modes of Bi1−xDyxFeO3 (x = 0.15) are assigned under orthorhombic (pnma) rather than rhombohedral (R3c) as the Rietveld analysis of X-ray diffraction data predicts a structural transformation for this particular composition. A complete suppression of two phonon modes has been noticed for this composition. An anomaly in the temperature dependent dielectric studies has been observed in all the samples at the vicinity of Neel temperature indicating a magnetic ordering, and an increase in magnetization with increase of Dy concentration in BiFeO3 is noticed from the room temperature magnetic studies. P–E hysteresis loop studies show a decrease of remnant polarization (Pr) with the increase in Dy concentration and disappearance of hysteresis loop occurs for Bi1−xDyxFeO3 (x = 0.15) depicting a transformation from non-centrosymmetric (R3c) to centrosymmetric (Pnma) system.

Investigation on transition behavior and electrical properties of (K0.5Na0.5)1-xLixNb0.84Ta0.1Sb0.06O3 around polymorphic phase transition region

(K0.5Na0.5)1-xLixNb0.84Ta0.1Sb0.06O3 (KNLNTS) lead free ceramics with different Li concentration were fabricated by conventional solid-state reaction method. By increasing Li ions in KNLNTS, the grains grow up and the crystal structure changes from orthorhombic to tetragonal. When 0.03 ≤ x ≤ 0.05, the ceramics structure lays in PPT region. Polarization versus electric field (P-E) hysteresis loops at room temperature show good ferroelectric properties and the remnant polarization decreases by increasing Li content while coercive electric keeps almost unchanged. In PPT region, taking x = 0.04 as an example, the sample shows excellent dielectric properties: the dielectric constant is 1159 and loss tangent is 0.04, while the piezoelectric constant d33 is 245 pC/N and kp is 0.44 at room temperature, it is promising for (K0.5Na0.5)1-xLixNb0.84Ta0.1Sb0.06O3 with 4 at. % Li to substitute PZT.

The unusual temperature dependence of the switching behavior in a ferroelectric single crystal with dislocations

The unusual temperature-induced switching behavior in a ferroelectric single crystal with dislocation arrays is investigated by using phase field simulations. The results show that the influence of temperature on the hysteresis loop of a ferroelectric is dependent on the dislocation arrays. In the presence of dislocation arrays, the dependence of the coercive field on the temperature is different from that of a dislocation-free ferroelectric. The coercive field increases when the temperature increases from room temperature to a critical temperature, which is attributed to the pinning of domains by the dislocation arrays. Above the critical temperature, both the coercive field and the remnant polarization decrease with temperature. It is found that double hysteresis loops can be induced by dislocation arrays when the temperature is higher than the Curie temperature. This work exhibits the complex role of temperature and dislocations in the polarization switching of ferroelectric single crystal.

Characterization and Rietveld Refinement of A-site deficient Lanthanum doped Barium Titanate

Abstract Ba 1− x La 2 x /3 TiO 3 (0.00 ⩽ x ⩽ 0.10, in a step of 0.02) ceramics have been prepared through solid state reaction route. Structural studies suggested a transition in phase from tetragonal to cubic symmetry with increase in Lanthanum content. Rietveld Refinement technique employed for investigation confirmed the same. Photoluminescence study revealed introduction of structural disorder by means of A-site vacancies and displacement of M–O bond leading to shallow defects. Optical band gap value calculated from UV–Vis spectra decreased with increase in La concentration. A drastic decrease in grain size of undoped BT was observed with introduction of La through Scanning Electron Micrographs. Dielectric studies were performed and a gradual decrease in the Curie temperature with increase in La content in coherence with structural studies was observed along with pinching effect. Normal ferroelectric character was obtained for the composition x = 0.00 to x = 0.06 while relaxor like behavior was observed for composition x ⩾ 0.08. The composition x = 0.10 made a good Vogel–Fulcher fit. Inhomogeneity induced in the BT lattice due to 8% La doping is strong enough to make an onset of such behavior. P ∼ E hysteresis loop showed a regular decrease in remnant polarization and coercive field featuring similar relaxor like behavior.