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Second harmonic generation (SHG) study of the phase transitions The temperature dependences of the SHG signal for a Ba4Nd2Ti4Nb6O30, b Ba4Sm2Ti4Nb6O30, and c Ba4Eu2Ti4Nb6O30, indicating the phase transitions from the high-temperature centrosymmetric nonpolar phase to the a centric polar phases for all the compositions
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Antiferroelectrics are of interest due to their high potential for energy storage. Here, we report the discovery of pinched, polarization-vs.-electric field (P–E) hysteresis loops in the lead-free tungsten bronze ferroelectrics Ba4Sm2Ti4Nb6O30 and Ba4Eu2Ti4Nb6O30, while a broad, single P–E hysteresis loop was observed in the analogue compound Ba4Nd...
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... It is observed that the P-E loops at low electric field (10,11,13, and 14 kV/cm) exhibit double hysteresis loops, as well as an almost linear P-E relationship in the middle section of the hysteresis loop. The double hysteresis loops in the present composite sample could be explained by the presence of random local strain and defect dipoles in the ferroelectric of BaTiO 3 lattice [49][50][51]. Additionally, the other source of the double hysteresis loops in this sample is the first-order ferroelectric transition occurring in the temperature range between the Curie-Weiss temperature (T 0 ) and the Curie temperature (T c ) [52]. ...
... Additionally, the other source of the double hysteresis loops in this sample is the first-order ferroelectric transition occurring in the temperature range between the Curie-Weiss temperature (T 0 ) and the Curie temperature (T c ) [52]. Therefore, in the first-order ferroelectric transition, double hysteresis loops are observed near T c , indicating the electric field-induced phase transition from paraelectric to ferroelectric [50]. This finding is confirmed by the aforementioned dielectric results for the present composite sample, where the phase transition in this sample is of the first order. ...
A transparent composite sample containing BaTiO3 was synthesized by using the melting quenching method. The presence of a glassy phase in this composite sample was detected through XRD analysis, and this was further confirmed by DSC study. TEM and SAED analyses provided evidence that the BaTiO3 nanoparticles/clusters are embedded within the borate glass matrix, establishing the composite nature of this sample. FTIR spectrum of the present sample revealed that the glass matrix is composed of two structural groups (BO3 with NBO’s, and BO4), along with the distinct groups for BaTiO3. XPS spectra of the present composite sample indicated the presence of more than one type of boron, barium, titanium and oxygen. DSC and dielectric studies of the present composite sample revealed the presence of the phase transition temperature (Tc). Dielectric constant (ɛr) and dielectric loss (tan δ) curves of the present composite sample displayed an anomaly peak in the vicinity of TC. The optical transmission spectrum of the present composite sample exhibit two transmission bands of Ti³⁺ (3d¹) ions in tetragonal distorted sites. At room temperature, the present transparent composite sample exhibited double hysteresis loops for BaTiO3 at low electric fields. The results obtained can be used for the development of lead-free ferroelectric material.
... As one of the main and unique properties of TTB, ferroelectricity has always been a focus of attention. [10][11][12][13][14][15][16][17][18][19][20][21] The origin of ferroelectricity in TTB is associated with the movement of B cations away from the center of oxygen octahedra along the c axis. Generally speaking, the ferroelectricity of TTB includes normal ferroelectricity and relaxor ferroelectricity, 10,11 and the crossover from normal ferroelectric to the relaxor in filled tungsten bronzes is determined by two factors: A-site order/disorder and the difference in A1/A2-site radii. ...
... [12][13][14] Recently, pinched P-E hysteresis loops have been detected in a series of TTB systems with various structure origins. Based on the detailed in situ TEM research, our previous work related to the pinched P-E hysteresis loops in Ba 4 R 2 Ti 4 Nb 6 O 30 (R = Sm and Eu) ceramics to the field-induced transition from a nonpolar, incommensurately modulated (IC) state to a polar, commensurately modulated phase, 15,16 and similar behaviors also exist in Ba 4 Sm 2 Fe 0.5 Ti 3 Nb 6.5 O 30 materials 17 and KSr 2 Nb 5 O 15 materials. 18 In the K 2 RNb 5 O 15 (R = Nd, Pr, and Gd) system, 19 the observed pinched P-E loops are related to a possible antiferroelectric order, while, in "empty" tetragonal tungsten bronze Ba 4 La 0.67 Nb 10 O 30 , pinched P-E loops are related to the structure disorder, which disrupts the long-range polar ordering. ...
... As the temperature approached the ferroelectric transition range, the pinched P-E loop gradually began to resemble the double hysteresis loop, while the remnant polarization (P r ) tended to approach zero. According to the previous work, 15,16 in tungsten bronze ferroelectrics with the pinched hysteresis loops, nonpolar IC modulation imbedded in the ferroelectric phase, and the field-induced transition from the nonpolar state to the polar state dominates the pinched loops and forms new field-induced ferroelectric domains. Therefore, the polarization reversal process in the present ceramics includes two kinds of ferroelectric domains, which are the original and field-induced ferroelectric domains. ...
Ferroelectric transition and polarization characteristics were explored for filled tungsten bronze Ba4Sm2Ti4Nb6O30 ceramics with pinched P–E hysteresis loops. Two dielectric permittivity peaks were observed at around 553 and 486 K on heating and cooling cycles, respectively, with a large thermal hysteresis (∼77 K), indicating the first-order ferroelectric phase transition behavior in the present ceramics. In addition, a low-temperature dielectric relaxation appeared at around 300 K, following the Vogel–Fulcher relationship, which is related to thermal activation related to the polarization in the ab plane. Pinched P–E hysteresis loops were detected in the temperature range of 293–453 K with two pairs of coercive fields, indicating certain polar reversal mechanism, while E1 corresponds to the reversal field needed for all the ferroelectric domains in the system, and E2 is the back switch field from the polar state to the nonpolar state. Therefore, (E1–E2)/2 is the effect coercive field for the polar domain induced by the field transition. Temperature dependence of the coercive fields E1, E2, and (E1–E2)/2 is fitted to the Vopsaroiu model with different activated energies obtained for different temperature ranges, based on which the polarization dynamics of the pinched hysteresis loops are discussed.
... As a result, it can be concluded from figure 4 that the ferroelectric performance of the HZO thin films is strongly correlated with the CTE mismatch between the HZO layer and the TE/BE. The constricted hysteresis loop of the W/HZO/Pt device ( figure 4(b)) may result from the coexistence of the nonferroelectric and ferroelectric crystalline phases in the HZO layer together with the presence of a built-in electric field due to the asymmetric TE and BE structure [49][50][51][52][53][54]. Because of the built-in electric field established by different WFs of the TE and BE in the W/HZO/Pt structure, the distribution of charged defects such as oxygen vacancies in the HZO layer is nonuniform, which may cause the difficulty in the motion of ferroelectric domain walls [52][53][54]. ...
In this study, platinum (Pt) and tungsten (W), two materials with dissimilar coefficients of thermal expansion (CTE) and work functions (WF), are used as the top electrode (TE) and the bottom electrode (BE) in metal/ferroelectric/metal (MFM) structures to explore the ferroelectricity of hafnium zirconium oxide (HZO) with a thickness less than 10 nm. The electrical measurements indicate that a higher CTE mismatch between HZO and TE/BE is beneficial for enhancing the ferroelectric properties of nanoscale HZO thin films. The different WFs of TE and BE generate a built-in electric field in the HZO layer, leading to shifts in the hysteresis loops and the capacitance-voltage characteristics. The structural characterizations reveal that the preferred formation of the orthorhombic phase in HZO is dominated by the W BE. The device in which W is used as the TE and BE (the W/HZO/W MFM structure) presents the optimal ferroelectric performance of a high remanent polarization (2 P r = 55.2 μC/cm2). The presence of tungsten oxide (WOx) at the W/HZO interfaces, as revealed by high-resolution transmission microscopy, is also responsible for the enhancement of ferroelectric properties. This study demonstrates the significant effects of different CTEs and WFs of TE and BE on the properties of ferroelectric HZO thin films.
... This dielectric material, similar to perovskites, comprises deformed BO 6 octahedra connected by corners, creating three distinct sites: triangular, square and pentagonal. The chemical formula can be written as (A2) 2 (A1)C 2 B 5 O 15 , where the A1 and A2 (pentagonal and square sites respectively) may be occupied by all or part of a larger cation such as Sr 2+ , Ba 2+ , Ca 2+ , Na + , or K + , B-site is filled by a high valence cation such as W 6+ , Nb 5+ or Ti 4+ , and the C site is usually vacant due to the gap being too small [11][12][13][14][15][16][17][18][19][20][21]. Among the tungsten bronze systems, the compound Ba 2 NaNb 5 O 15 (BNN) has recently received much attention [12,13,22,23]. ...
The effects of Na+ substitution by Y3+ on the structural, microstructural, dielectric and electrical properties of Ba2Na(1-3x)YxNb5O15 compositions with (x= 0, 0.02 and 0.04 ) have been studied in detail. The solid solutions of different compositions were prepared by the solid state reaction route method and characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Complex Impedance Spectroscopy (CIS) techniques. The XRD study confirmed that all prepared compositions have a single-phase orthorhombic tungsten bronze structure with space group Cmm2 at room temperature. The microstructural studies revealed a grain shape and size change in response to increasing Y3+ concentration. The dielectric properties of the obtained compositions are evaluated over a temperature range of 40 to 600 °C. The dielectric properties were improved for the Y2O3-substituted Ba2NaNb5O15 compound compared to the undoped Ba2NaNb5O15 compound. The non-Debye type relaxation mechanism is confirmed by the -Z'' versus Z' traces. The grain contribution was studied using an equivalent electrical circuit with a Resistor R, a Capacitor C, and a Constant-Phase Element CPE in parallel, in the absence of the grain boundary response and the electrode effect in the frequency range 10 Hz-1MHz. The experimental AC conductivity data were evaluated by using Jonscher's power law. The activation energies obtained from the relaxation and conduction processes, present two different regions as a function of temperature related to the two electrical processes for the prepared ceramics.
... In Ba 4 R 2 Ti 4 Nb 6 O 30 (R = Nd, Sm, Eu), the pinched P-E hysteresis loops are attributed to the field-induced transition from a non-polar incommensurate state to a polar commensurate state. 9,10 Thus, it can be seen that the tailoring and design of A-site ions in tungsten bronze materials is the key to triggering rich physical properties. ...
... 22,24 The low temperature ferroelectric phase has the non-centrosymmetric structure with P4bm space group, accompanied by commensurate modulation structure, like Ba 4 Nd 2 Ti 4 Nb 6 O 30 . 9,22,23 In the thermal hysteresis temperature range of a first-order ferroelectric transition, coexistence of ferroelectric and paraelectric phases is accompanied by the coexistence of commensurate and incommensurate modulation structures. In some cases, like Ba 4 Sm 2 Ti 4 Nb 6 O 30 and Ba 4 Eu 2 Ti 4 Nb 6 O 30 , the coexistence of commensurate and incommensurate modulation structures was observed at temperatures far below the phase transition range, combined with typical pinched P-E hysteresis loops. ...
... ceramics, which is attributed to electric field-induced phase transition between nonpolar incommensurate phase and polar commensurate phase. 9 Recently, Murata et al. 29 observed a double-hysteresis loop in tetragonal tungsten bronze K 2 RNb 5 O 15 (R: rare earth) and attributed two dielectric anomalies to two phase transitions from ferroelectric to antiferroelectric to paraelectric, and demonstrated two different types of antipolar displacement patterns (Γ À 2 and M þ 1 M þ 4 ) by firstprinciples calculations. Krayzman et al. 30 reported that polar Γ À 3 and antipolar Γ À 2 modes can simultaneously exist above the nominal ferroelectric transition temperature of 350 K in tetragonal tungsten bronzes with incommensurate modulate structure, probably showing antiferroelectric behavior with elevated temperatures. ...
A-site high entropy Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 tungsten bronze ceramics were designed and prepared by a standard solid state sintering process. First-order ferroelectric transition occurs around 240 °C on heating, while around 136 °C on cooling. Pinched and asymmetric P–E hysteresis loops were observed within and below the thermal hysteresis temperature range of the ferroelectric transition. Pinched P–E hysteresis loops were attributed to the coupling between the ferroelectric transition and the commensurate/incommensurate modulation transition. The reason for the asymmetry of the hysteresis loop was the presence of an internal bias electric field. Different measuring procedures were designed to clarify the evolution of hysteresis loop asymmetry. The existence of oxygen vacancy and Eu3+/Eu2+ was identified by x-ray photoemission spectroscopy. The electric field cycling with elevated temperatures caused defect dipoles incline to align along the direction of spontaneous polarization leading to the internal bias electric field. Due to the A-site high entropy effect, dielectric strength of Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 ceramics is up to 300 kV/cm, which is increased by more than 50% than that with the single element in the A1-site.
... For example, in AFE compositions in the PbZr 1−x Ti x O 3 (PZT) system, an incommensurate structure is observed in transmission electron microscopy (TEM) images and it has been suggested that the incommensurate phase results from competition between long-range FE and AFE orders. 26 Similarly, double hysteresis loops seen in the P−E data at temperatures far below T C , for Ba 4 Sm 2 Ti 4 Nb 6 O 30 and Ba 4 Eu 2 Ti 4 Nb 6 O 30 , 28 have been suggested to be caused by field-induced transitions between polar 14,18 Thus, it is suggested here that in STLT32, a field-induced transition occurs between a weakly polar phase and a more strongly polar phase. Figure S8 shows the normalized dielectric permittivity change in STLT32 with DC bias field. ...
Antiferroelectric (AFE) materials have been intensively studied due to their potential uses in energy storage applications and energy conversion. These materials are characterized by double polarization-electric field (P-E) hysteresis loops and nonpolar crystal structures. Unusually, in the present work, Sr1.68La0.32Ta1.68Ti0.32O7 (STLT32), Sr1.64La0.36Ta1.64Ti0.36O7 (STLT36), and Sr1.85Ca0.15Ta2O7 (SCT15), lead-free perovskite layered structure (PLS) materials, are shown to exhibit AFE-like double P-E hysteresis loops despite maintaining a polar crystal structure. The double hysteresis loops are present over wide ranges of electric field and temperature. While neutron diffraction and piezoresponse force microscopy results indicate that the STLT32 system should be ferroelectric at room temperature, the observed AFE-like electrical behavior suggests that the electrical response is dominated by a weakly polar phase with a field-induced transition to a more strongly polar phase. Variable-temperature dielectric measurements suggest the presence of two-phase transitions in STLT32 at ca. 250 and 750 °C. The latter transition is confirmed by thermal analysis and is accompanied by structural changes in the layers, such as in the degree of octahedral tilting and changes in the perovskite block width and interlayer gap, associated with a change from non-centrosymmetric to centrosymmetric structures. The lower-temperature transition is more diffuse in nature but is evidenced by subtle changes in the lattice parameters. The dielectric properties of an STLT32 ceramic at microwave frequencies was measured using a coplanar waveguide transmission line and revealed stable permittivity from 1 kHz up to 20 GHz with low dielectric loss. This work represents the first observation of its kind in a PLS-type material.
... Non-linear relaxor materials were investigated in a wide range of researchers due to their outstanding properties for piezoelectric and electromechanical applications. Ferroelectrics are a very important family of functional materials, and they have received attention from a variety of fields, including material science, condensed matter physics and electric engineering [1]. The ability of non-linear dielectric materials on the charges controlling and energy storage can be described by how the material can tend to polarized in the presence of electric field which refers to poling effect [2]. ...
... The pinched P-E hysteresis loops in defect-free ferroelectrics are often linked to a high piezoelectric response, but the mechanisms of these phenomena are diverse. Therefore, searching for pinched P-E hysteresis loops in more ferroelectric materials and revealing their mechanisms are of high scientific interest and importance [1]. ...
Electric field-induced phase transitions are the most important characteristics of relaxor, ferroelectric and anti-ferroelectric
materials, while the origin of this behavior in relaxor materials is poorly understood. In the present study, an electric
field dependent on the structural, the dielectric, and the ferroelectric properties of 0.7[(Bi0.5Na0.3K0.2)TiO3]-0.2SrTiO3-
0.1(Ba0.8Ca0.2)TiO3](BNKT-ST-BCT) relaxor ceramic has been performed. In the absence of the poling effect, a normal
transition from relaxor to para-electric phase occurs at Burns temperature TB
~ 100 °C. However, at high electric field of
the poling (E = 50 kV/cm, T = 80 °C, t = 15 min), two-step transitions were found: the first one is a ferroelectric–relaxor
transition at depolarization temperature (
Td ~ 100 °C), and the second one is a relaxor–para-electric transition at higher
temperatures (
TB = 150 °C). Increasing the Burns temperature by applying field is due to the residual polarization effect. At
lower electric field (E < 15 kV/cm), a relaxor behavior with pinched P–E loop was observed caused by man intrinsic effect,
where ST induced phase transition from a non-polar incommensurate to a polar commensurately modulated crystal structure.
The sample exhibited a relaxor–ferroelectric phase transition as manifested by a change of the domain structure from
polar nano-region PNR with short-range order (SRO) to coarse ferroelectric Lamellar domain with long-range order (LRO)
at high applied cycle of electric field above the domain switching field. The change of the domain structure is contributed
to domain growth caused by domain wall displacement effect. These results were confirmed by XRD of poled ceramic at
different poling conditions (E = 0.0–58 kV/cm) near the phase transition temperature.
... The observed peaks splitting in J-E loops could be due to the coexistence of the polar and nonpolar phases, which reversibly switch by applying the electric field. [53][54][55] In addition, Fig. 6c illustrates the room-temperature bipolar S-E plots of the xBTSn samples. Relatively symmetric butterfly-like-shaped S-E curves were observed for all samples due to the lattice's electromechanical strain and related to the switching and movement of the domain walls by the applied electric field. ...
The design of lead-free ceramics for piezoelectric energy harvesting applications become a hot topic. Among these materials, Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) and BaTi0.89Sn0.11O3 (BTSn) are considered as potential candidates due to their enhanced piezoelectric properties. Here, the structural, electrical and piezoelectric energy harvesting performances of the (1−x)Ba0.85Ca0.15Zr0.10Ti0.90O3–xBaTi0.89Sn0.11O3 (xBTSn, x=0.2, 0.4 and 0.6) system are investigated. A systematic study of the structural properties of the xBTSn samples was carried out using X-ray diffraction, Raman spectroscopy, and dielectric measurements. The addition of BTSn allows a successive phase transition, which broadens the application temperature range. The enhanced piezoelectric energy harvesting properties were found in 0.2BTSn ceramic, where the large-signal and small-signal piezoelectric coefficients, piezoelectric voltage and the piezoelectric figure of merit reached 245 pm V−1, 228 pC N−1, 16.2 mV m N−1 and 3.7 pm2 N−1), respectively. Consequently, the combination of BCZT and BTSn could provide suitable lead-free materials with enhanced piezoelectric energy harvesting performances.
... The rare-earth dopants act as the luminescent centers in the dielectric matrixes. Meanwhile, the dopants also caused the incommensurate/commensurate displacive modulations, and influenced the relaxor/ferroelectric behavior of the tungsten bronze structured matrix, which further affected the electric-luminescent coupling features [21][22][23]. Hence, understanding the effect of rare-earth doping on the electric properties of hosts is also very important, especially at a doping level similar to luminescent studies. ...
... The A1and A2-sites can be occupied by alkaline metals, alkaline-earth metals or rare-earth metals, whereas the C-site remains empty due to the size limit. Based on previous studies [21][22][23], the ferroelectric transition and dielectric relaxation behaviour of filled tungsten bronzes were dominated by the radius relationships between A1-and A2-cations. Lima et al. exhibited that rare-earth dopants principally occupied the A1-site in the KSN lattice [18]. ...
... %, the shape of P-E loops tended to be saturated, the P r and E c enhanced. Based on the study of Li et al. [23], the pinched P-E loops are ascribed to the electric-field-induced phase transition from non-polar incommensurate to polar commensurate modulation of crystal structure in tungsten bronzes. Hence, the related changes of the P-E loops can be attributed to the structural modulation caused by the Sm 3+ doping. ...
The luminescence modulation behavior of lanthanide ion doped materials possesses great potential for applications in sensing, display and anti-counterfeiting devices. Unlike traditional tuning methods for chemical compositions, novel rare-earth doped ferroelectric oxides exhibit attractive luminescence modulation effects via electric polarization engineering, and enrich the development of multifunctional devices. In this work, Sm³⁺ doped KSr2Nb5O15 ceramics with abundant ferroelectric and luminescent properties were synthesized. The samples show different relaxation behaviors and ferroelectric features upon chemical and structural factors caused by Sm³⁺ doping, such as average ionic radii, local tolerance factors, and chemical bonds. After polarization at 20 kV/cm for 20 min, a considerable increase (∼40%) in the luminescent emission intensity was obtained in 4 mol. % Sm³⁺ doped KSr2Nb5O15 ceramics. The related luminescence modulation mechanism was attributed to controlling the environmental symmetry around Sm³⁺ by the electric polarization.
... In a related modelling study, Sheldon and Di Ventra [81] showed that activation of disordered memristive networks with strong memory (G on / G off ≫ 1), with an electrical 'crack' appearance, is consistent with a discontinuous (first-order) phase transition, rather than a continuous (secondorder) transition, which is a hallmark of criticality [82]. First-order phase transitions are indicated by hysteresis and have also been observed in ferroelectrics [83] and in models of spiking neural networks [84]. For a randomly diluted lattice network, the authors also found avalanches with power-law size distributions, similar to that observed in neuronal population cultures [34], with an exponent that converges towards the value predicted by mean-field-theory as network size increases. ...
Nanowire networks represent a unique class of neuromorphic systems. Their self-assembly confers a complex structure to their network circuitry, embedding a higher interconnectivity of resistive switching memory (memristive) cross-point junctions than can be achieved with top-down nanofabrication methods. Coupling of the nonlinear memristive dynamics to the network topology enables intrinsic adaptiveness and gives rise to emergent non-local dynamics. In this article, we summarise the physical principles underlying the memristive junctions and network dynamics of neuromorphic nanowire networks and provide the first comprehensive review of studies to date. We conclude with a perspective on future prospects for neuromorphic information processing.
