Ferroelectric phase transition and electrical conduction mechanisms in high Curie-temperature PMN-PHT piezoelectric ceramics

Ferroelectric phase transition characteristic and electrical conduction mechanism of the high Curie-point (T_C) 0.15Pb(Mg_1/3Nb_2/3)O₃−0.4PbHfO₃−0.45PbTiO₃ (PMN-PHT) piezoelectric ceramics were studied by the temperature dependent Raman spectra and electrical properties. Sole first-order ferroelectric phase transition is demonstrated by the thermal hysteresis behavior of the temperature dependent dielectric constant and the dramatic drop of the derivative of inverse dielectric constant ξ= d(1/ε_r)/dT around T_C in the PMN-PHT ceramics. The temperature dependent Raman spectroscopy not only provides further evidence for the ferroelectric to paraelectric phase transition appearing around T_C in the PMN-PHT ceramics, but also reveals the successive phase symmetry changes of the polar nanoregions (PNRs), in which apparent anomalies appear in the Raman peaks' wavenumber, wavenumber distance, intensity, intensity ratio, and line width of some selected Raman modes upon heating. Typical sole cole-cole circle is obtained for the PMN-PHT ceramics in the temperature range of 440–560 °C, based on which the activation energy (E_a) of the electrical conduction is calculated being ~1.2 eV. Such low value of E_a indicates that the oxygen vacancies formed in the PHT-PMN ceramics induced by the evaporation of Pb during the sintering process dominate the high-temperature extrinsic electrical conduction.     

Anisotropic domain structures of Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 single crystals with high ferroelectric phase transition temperature

The anisotropic domain structures and local piezoresponse of rhombohedral Pb(Mg_1/3Nb_2/3)O₃–PbZrO₃–PbTiO₃ single crystals with high ferroelectric phase transition temperature (T_FE‐FE≥120°C) were systematically investigated by vector piezoresponse force microscopy. The typical size of labyrinthine domain pattern for [001]_C sample was in the range of 100‐200 nm, revealing its relaxor feature. While the [011]_C sample exhibited ordered ribbon‐shaped domain pattern with preferential alignment along <011> direction since the modulation effect of polar nanoregions. For [111]_C sample, it had messy and featureless domain patterns. For as‐grown crystal, the incorporation of Zr⁴⁺ cation in Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ system resulted in that the long‐range coulomb interactions of the charged ions in the short range order regions were weakened, leading to an increased relaxor feature. Concurrently, the incorporation of Zr⁴⁺ cation enhanced the Pb‐B repulsion intensity, resulting in an improved T_FE‐FE. Temperature‐dependent properties of as‐grown crystal exhibited good temperature stability from 30 to 120°C, indicating it is a promising material for actuator and ultrasonic transducer applications.     

Effect of electric poling on structural,magnetic and ferroelectric properties of 0.8PbFe0.5Nb0.5O3-0.2BiFeO3 multiferroic solid solution

The effect of electric poling on structure, magnetic and ferroelectric properties of 0.8PbFe_0.5Nb_0.5O₃-0.2BiFeO₃ (0.8PFN-0.2BFO) multiferroic was studied through XRD, Raman, magnetic and ferroelectric measurements. Single step solid state reaction method was adopted to synthesize single phase 0.8PFN-0.2BFO multiferroic at lower calcination and sintering temperature. Room temperature (RT) XRD pattern before and after poling confirmed the monoclinic structure with Cm space group. Rietveld refined XRD for poled and unpoled sample shows the influence of electric poling on Fe-O1, Fe-O2, Nb-O and Bi-O modes. There is a small variation in the lattice parameters after electric poling. The structural properties were also studied in detail for the poled and unpoled 0.8PFN-0.2BFO using Raman spectroscopy. Raman measurements were carried out over a wide range of temperature (250–550 K) for both poled and unpoled samples. At RT unpoled 0.8PFN-0.2BFO multiferroic exhibit 8 active modes at 211, 263, 440, 484, 571, 706, 785 and 1120 cm^-1 in the frequency range 100–1200 cm^-1. The Raman peaks exhibits significant changes in intensity as well as shape of the spectra at the characteristic temperature T_C (470 K) and T_N (310 K). Poled Raman spectra show major changes in the Fe/Nb-O modes intensities around T_N and are due to dynamic nature of spin phonon coupling. Changes observed in the temperature dependent magnetic measurements i.e. ZFC/FC and M − H loop evidence the existence of converse magneto-electric coupling (CME) and this is due to the poling effects on Fe-O, Nb-O active modes. Due to rotation of the oxygen octahedral the electric field induced strain will originate in the system. P-E loops after poling show an increase in remnant polarisation and coercive field due to an improvement in domain ordering. The potential tunability of magnetisation with electric poling is an ideal tool for realisation of application in practical devices.     

Effect of Sb-dopant on phase transitions and selected properties of lead zirconate ceramics

The effect of antimony dopant on AFE–FE and FE–PE phase transitions in the lead zirconate ceramics was investigated by differential thermal analysis, pyroelectric and dielectric measurements. The decrease of these phase transition temperatures was observed without change in width of temperature range in which the intermediate ferroelectric phase occurs. This effect is different from this one observed in the PbZrO₃ ceramics with other heterovalent substitutions such as La³⁺, Ta³⁺ and Nb⁵⁺ previously studied. The effect of Sb-dopant on P_r(T) and ε(T) characteristics, and in particular low frequency dielectric dispersion in paraelectric phase is more detailed discussed.     

Dynamic of polar nanoregions and its impact on the pyroelectric and dielectric properties in paraelectric KTN materials

The origin of the excellent properties of KTN-based materials around Curie temperature (T_C), which should be originated form the motion of polar nanoregions (PNRs), has attracted considerable research interest. In this paper, the relaxation of a KTa_0.63Nb_0.37O₃ single crystal is discussed with the temperature dependence of permittivity. Moreover, its pyroelectric effect above T_C is investigated. In detail, the pyroelectric coefficient decreases from ∼110.0 to ∼13.0 μC/(m² K), with the temperature increasing from 22 to 33°C, and finally reduces to 0 at 100°C with PNRs disappear. Moreover, the dynamic dielectric nonlinearity for the KTN single crystal is studied in the paraelectric phase. To investigate these mechanisms, the amplitude and phase angle of the first and third harmonics under various electric fields, frequencies, and temperatures are analyzed. As a result, the motions of PNRs induced by electric field, which is pinned and depinned by the defect, are presented to explain the nonlinear dielectric response observed in the paraelectric KTN single crystal.     

Relaxation dynamics,phase pattern in the vicinity of the Curie temperature,Fe valent state and the Mössbauer effect in PFN ceramics

High-density lead ferroniobate, PbFe_1/2Nb_1/2O₃ (PFN), was prepared by the conventional ceramic technology. Its dielectric properties, phase pattern in the vicinity of transition into the polar phase, and the x-ray electron and Mössbauer spectra were studied. The relaxation dynamics discovered at the temperature exceeding the Curie temperature at the frequencies of 3×10⁻²–10⁵ Hz is described in detail. Near T_C, the following sequence of phase transitions was established: rhombohedral (T<368 K)→pseudocubic (368 K<T<387 K)→cubic (T>387 K). It is shown that in both the ferroelectric and paraelectric phases the Fe ions are, mainly, in a high-spin valent state Fe³⁺ in the octahedral environment.     

Effect of Niobium Oxide on the Structure and Properties of Melt‐Derived Bioactive Glasses

The effects of adding Nb₂O₅ on the physical properties and glass structure of two glass series derived from the 45S5 Bioglass^® have been studied. The multinuclear ²⁹Si, ³¹P, and ²³Na solid‐state MAS NMR spectra of the glasses, Raman spectroscopy and the determination of some physical properties have generated insight into the structure of the glasses. The ²⁹Si MAS NMR spectra suggest that Nb⁵⁺ ions create cross‐links between several oxygen sites, breaking Si–O–Si bonds to form a range of polyhedra [Nb(OM)_6?y(OSi)_y], where 1 ≤ y ≤ 5 and M = Na, Ca, or P. The Raman spectra show that the Nb–O–P bonds would occur in the terminal sites. Adding Nb₂O₅ significantly increases the density and the stability against devitrification, as indicated by ΔT(T_x ? T_g). Bioglass particle dispersions prepared by incorporating up to 1.3 mol% Nb₂O₅ by replacing P₂O₅ or up to 1.0 mol% Nb₂O₅ by replacing SiO₂ in 45S5 Bioglass^® using deionized water or solutions buffered with HEPES showed a significant increase in the pH during the early steps of the reaction, compared using the rate and magnitude during the earliest stages of BG45S5 dissolution.     

Structures and pyroelectric properties for [111]-oriented Mn-doped rhombohedral 0.36PIN-0.36PMN-0.28PT crystal

The crystal structures, pyroelectric properties, and thermal stability of [111]-oriented 0.5 mol% Mn-doped 0.36Pb(In_1/2Nb_1/2)O₃-0.36Pb(Mg_1/3Nb_2/3)O₃-0.28PbTiO₃ (Mn-0.36PIN-0.36PMN-0.28PT) ternary single crystal were investigated. The temperature dependence of the Raman spectra and dielectric properties revealed that the crystal exhibited a rhombohedral (R) structure at room temperature, and ferroelectric R → tetragonal (T) and ferroelectric T to paraelectric cubic (C) phase transitions at 130 and 175°C respectively. The single crystal had a high remnant polarization of P_r = 38 μC cm^–2 and coercive field of E_C = 12 kV cm^–1 at room temperature and a frequency of f = 100 Hz. The values of P_r and E_C decreased with increasing temperature, exhibiting anomalies near their phase-transition temperatures, which coincided with changes in the Raman spectra and dielectric properties. Furthermore, at 25°C and f = 100 Hz, the single crystal had high pyroelectric coefficients of p = 8.7 × 10⁻⁴ C m⁻² K⁻¹, figures of merit for the current responsivity of F_i = 3.5 × 10⁻¹⁰ m V⁻¹, the voltage responsivity of F_v = 0.08 m² C⁻¹, and the detectivity of F_d = 30.1 × 10⁻⁵ Pa^−1/2. These values were weakly dependent on temperature below 120°C. In addition, the room-temperature pyroelectric coefficients of the ternary single crystal maintain over 83% of the original value at thermal annealing temperatures below 120°C. These outstanding pyroelectric properties, together with high thermal stability, indicate that [111]-oriented rhombohedral Mn-0.36PIN-0.36PMN-0.28PT ternary single crystal is a new potential candidate for infrared detection applications.     

Orientation-dependent electrical property and domain configuration of Mn-doped Pb(In0.5Nb0.5)O3–PbTiO3 single crystal

Orientation dependence of electrical properties and domain configurations of 8 mol% Mn-doped rhombohedral PIN-PT (0.68Pb(In_0.5Nb_0.5)O₃–0.32Pb(Ti_0.92Mn_0.08)O₃) rhombohedral single crystals were investigated with an emphasis on studying the variations of coercive field (E_C), internal field (E_i) on domain patterns. Our results showed that for both [001] and [110]-oriented samples, the coercive field and internal field decreased with temperature (T) increasing in rhombohedral phase, and a peak appeared above rhombohedral-tetragonal phase transition temperature (T_RT). The abnormal peaks between T_RT and Curie temperature on E_C-T and E_i-T plots are explained by taking into consideration the ferroelectric phase transition and variation of defect polarization, which provides assistant comprehension on the dynamic of defect dipoles during phase transition at high temperature. Bubble- and ribbon-like domain patterns were observed in (001)- and (110)-plane, respectively, and smaller value of short-length correlation radius in (001)- plane indicates less aggregation of polar nanoregions in this crystallographic plane than that in (110)-plane.     

Low‐temperature sintering and electrical properties of Sr2Nb2O7 piezoceramics by CuO addition

Effects of 0.5 wt% CuO addition on the sintering, structural and electrical properties of perovskite layer structured (PLS) Sr₂Nb₂O₇ ceramics prepared by solid‐state reaction method are investigated. The addition of CuO is beneficial to the liquid phase bridge formation at sintering process, leading to lower sintering temperature of 1180°C and larger bulk density up to 98%. Meanwhile, CuO modified Sr₂Nb₂O₇ ceramics show a remarkable d₃₃ of (1.1 ± 0.1) pC/N while still with a very high T_c of (1340 ± 2)°C. Raman spectra indicate that the improvement of piezoelectricity could be attributed to the rotation and/or distortion of oxygen octahedron caused by possible Cu²⁺ substitution at the A‐sites of Sr₂Nb₂O₇.     

Enhanced electrical properties and strong red light‐emitting in Eu3+‐doped Sr1.90Ca0.15Na0.9Nb5O15 ceramics

The luminescent‐ferroelectic materials based on Sr_1.90Ca_0.15Na_0.9Nb₅O₁₅ (SCNN) matrix doping with Eu³⁺ were synthesized by the conventional solid‐state reaction method. The crystal structure, photoluminescence, thermal stability, dielectric, ferroelectric, and piezoelectric behaviors were systematically investigated. XRD results revealed that Eu³⁺ introduction could induce the tungsten bronze phase transition from orthorhombic to tetragonal structures. The dielectric spectra of all specimens showed two broad dielectric anomalies: a high‐temperature ferroelectric phase transition (T_c) and a low‐temperature ferroelastic phase transition (T_s), both of which were suppressed at higher Eu³⁺ concentrations. The enhanced electrical properties were obtained in a proper Eu³⁺ concentration range of 0.03‐0.05. For all SCNN:xEu³⁺ samples, the strong red emission peak at 617 nm originating from the electric dipole transition of ⁵D₀ →⁷F₂ was excited by different light excitations of 395 or 463 nm. Our results demonstrated that Eu³⁺‐doped SCNN materials might have promising potential in advanced multifunctional optoelectronic applications.     

Enhanced electrical properties related to structural distortion of CaBi2Nb2O9-based piezoelectric ceramics

CaBi₂Nb₂O₉ (CBN)-based high Curie temperature piezoelectric ceramics with formula Ca_0.8-xSr_x(Li_0.5Ce_0.15Bi_0.35)_0.2Bi₂Nb_1.94Ta_0.04W_0.02O₉ were prepared by conventional solid-state reaction method. The effects of strontium substitution for calcium in CBN pseudo-perovskite structure A-site were systematically studied. Results showed that the addition of Sr²⁺ ions lead to an improvement of the tetragonality of lattice structure, which resulted in an enhancement of piezoelectric and ferroelectric properties together with high Curie temperature T_C and good resistance to thermal depolarization. The analysis of dielectric spectrums revealed that the space charge polarization induced an additional dielectric anomaly occurred below T_C. The composition with x = 0.025 showed good integrated performance, the piezoelectric coefficient d₃₃ and T_C were ~17.5 pC/N and ~917°C, respectively. Even though the as-studied ceramics underwent high depolarizing temperature reached up to 875°C, d₃₃ decreased by 8% merely. The remanent polarization 2P_r and the resistivity ρ at 650°C were on the order of ~10 μC/cm² and 3 × 10⁵ Ω cm, respectively.     

Two‐Dimensional Nb‐Based M4C3 Solid Solutions (MXenes)

Herein, two new two‐dimensional Nb₄C₃‐based solid solutions (MXenes), (Nb_0.8,Ti_0.2)₄C₃T_x and (Nb_0.8,Zr_0.2)₄C₃T_x (where T is a surface termination) were synthesized—as confirmed by X‐ray diffraction—from their corresponding MAX phase precursors (Nb_0.8,Ti_0.2)₄AlC₃ and (Nb_0.8,Zr_0.2)₄AlC₃. This is the first report on a Zr‐containing MXene. Intercalation of Li ions into these two compositions, and Nb₄C₃T_x was studied to determine the potential of those materials for energy storage applications. Lithiation and delithiation peaks at 2.26 and 2.35 V, respectively, appeared in the case of Nb₄C₃T_x, but were not present in Nb₂CT_x. After 20 cycles at a rate of C/4, the specific capacities of (Nb_0.8,Ti_0.2)₄C₃T_x and (Nb_0.8,Zr_0.2)₄C₃T_x were 158 and 132 mAh/g, respectively, both slightly lower than the capacity of Nb₄C₃T_x.     

Local Structural Rearrangements and Evolution of Relaxor State in the Complex Perovskite (Ba1−xPbx) (In0.50Nb0.50) O3

Local structural rearrangements in lead‐based complex perovskites of the type (Ba_1?xPb_x)(In_0.50Nb_0.50)O₃ responsible for transition from ferroelectric [Ba(In_0.50Nb_0.50)O₃] to relaxor [Pb(In_0.50Nb_0.50)O₃] are examined by careful analysis of their Raman spectra. Subtle changes in the bonding brought about by the differences in the chemical nature of A‐ and B‐site cations have been correlated with the dynamic A–O–B coupling. Deviations in the local structure as a result of such bonding preferences have been confirmed by studying the changes in the Raman spectra when Nb⁵⁺ is substituted by Sn⁴⁺ as the third B‐site cation.     

Local phenomena in bismuth sodium titanate perovskite studied by Raman spectroscopy

In this work, 0.8Na_0.5Bi_0.5TiO₃‐0.2K_0.5Bi_0.5TiO₃ (BNKT) is studied by electrical characterizations, in situ Raman spectra in conjunction with the phenomenological Landau predictions to reveal the local phenomena. An electric field‐induced nonergodic relaxor‐to‐ferroelectric phase transition and domain switching start to take place at a critical field of 3 kV/mm. The polar phase was disrupted into the disordered relaxor phase at ferroelectric‐relaxor transition temperature (T_FR) along with the discontinuous phonon anomalies caused by the decoupling between the off‐centered Bi and Ti cations. The R3c and P4bm polar nanoregions (PNRs) can coexist in a wide temperature range and can be transformed reversibly below the temperature of dielectric maximum (T_m). The broad Raman bands were found to persist in high‐temperature paraelectric state induced by the existence of off‐centered Ti cation and ferroically deformed TiO₆ octahedra. A phenomenological Landau model and local structural evolution sequence at different thermal history were proposed to further elucidate the underlying mechanisms. This work will be conducive to understanding the local structure‐physical property correlations of high‐performance lead‐free piezoelectrics.     

Influence of molecular weight on dynamic crossover temperature in linear polymers

Dielectric and light scattering spectra of two linear polymers, polyisoprene (PIP) and polystyrene (PS), were analyzed in broad temperature and frequency range above the glass transition temperature, T_g. The crossover temperature, T_C, was estimated using two approaches: (i) derivative analysis of relaxation times proposed by Stickel and (ii) Mode-Coupling Theory approach. Both estimates provide consistent values. T_C varies with molecular weight (MW) in both polymers, while the ratio T_C/T_g changes significantly with MW in PS only. It appears that the segmental relaxation time at T_C has value τ(T_C) ∼ 10⁻⁷ s for both polymers independent of MW and similar to the value reported for many non-polymeric glass-forming systems. No sign of the dynamic crossover has been observed in the chain relaxation around T_C of the segmental dynamics.     

Electric field-induced phase transition and energy storage performance of highly-textured PbZrO3 antiferroelectric films with a deposition temperature dependence

Thin PbZrO₃ (PZO) antiferroelectric films with (001)-preferred orientation were deposited on SrRuO₃/Ca₂Nb₃O₁₀-nanosheet/Si substrates using pulsed laser deposition. Variation of the deposition temperature was found to play a key role in the control of the microstructure and strongly influence the energy storage performance of the thin film. The critical phase switching field, where the aligned antiferroelectric (AFE) domains start to transform into the ferroelectric (FE) state, decreased with increasing temperature. On the other hand, the content of the FE phase in the AFE PZO thin films increased with increasing deposition temperature. A large recoverable energy-storage density of 16.8?J/cm³ and high energy-storage efficiency of 69.2% under an electric field of 1000?kV/cm were achieved in the films deposited at 525?°C. This performance was due to the high forward switching field and backward switching field values and the low difference between these two fields. Moreover, the PZO thin films showed great charge-discharge cycling life with fatigue-free performance up to 10¹⁰ cycles and good thermal stability from room temperature to 100?°C.     

Ferroelectric phase transition and electrical properties of high-TC PMN-PH-PT ceramics prepared by partial oxalate route

The high-Curie temperature (T_C) 0.15Pb(Mg_1/3Nb_2/3)O₃-0.38PbHfO₃-0.47PbTiO₃ (PMN-PH-PT) piezoelectric ceramics were prepared by the partial oxalate route via the B-site oxide mixing method. The obtained uniform nm-sized PMN-PH-PT precursor powders provide high calcining and sintering activity for synthesizing ceramics, based on which the synthesis conditions were tailored as calcining at 775 °C and sintering at 1245 °C. The partial oxalate route synthesized PMN-PH-PT ceramics are far superior to the counterparts synthesized by the columbite precursor method and exhibit excellent thermal stability of the piezoelectric properties under T_C (～292 °C), ensuring the potential application in transducers under elevated environmental temperatures. The temperature dependent Raman spectroscopy not only proves the occurrence of the ferroelectric to paraelectric phase transition around T_C, but also confirms the successive phase symmetry transitions, which correlate with the polar nanoregions (PNRs) and/or the coexistence of multiple ferroelectric phases, revealing the origin of the enhanced electrical properties in the PMN-PH-PT ceramics.     

High‐Performance Small‐Amount Fe2O3‐Doped (K,Na)NbO3‐Based Lead‐Free Piezoceramics with Irregular Phase Evolution

[(K_0.43Na_0.57)_0.94Li_0.06][(Nb_0.94Sb_0.06)_0.95Ta_0.05]O₃ + x mol% Fe₂O₃ (KNLNST + x Fe, x = 0~0.60) lead‐free piezoelectric ceramics were prepared by conventional solid‐state reaction processing. The effects of small‐amount Fe₂O₃ doping on the microstructure and electrical properties of the KNLNST ceramics were systematically investigated. With increasing Fe³⁺ content, the orthorhombic‐tetragonal polymorphic phase transition temperature (T_O‐T) of KNLNST + x Fe ceramics presented an obvious “V” type variation trend, and T_O‐T was successfully shifted to near room temperature without changing T_C (T_C = 315°C) via doping Fe₂O₃ around 0.25 mol%. Electrical properties were significantly enhanced due to the coexistence of both orthorhombic and tetragonal ferroelectric phases at room temperature. The ceramics doped with 0.20 mol% Fe₂O₃ possessed optimal piezoelectric and dielectric properties of d₃₃ = 306 pC/N, k_p = 47.0%, = 1483 and tan δ = 0.023. It was revealed that the strong internal stress in the KNLNST + x Fe ceramics with higher Fe³⁺ contents (x = 0.40, 0.60) stabilized the orthorhombic phase, leading to the irregular “V” type rather than the usually observed monotonic phase transition with composition change in the ceramics.     

Processing and electromechanical properties of high-coercive field ZnO-doped PIN-PZN-PT ceramics

This study explores sintering and piezoelectricity of ZnO-doped perovskite Pb(In_1/2Nb_1/2)O₃-Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PZN-PT) ceramics. The enhanced densification of ZnO-doped PIN-PZN-PT is attributed to the formation of oxygen vacancies by the incorporation of Zn²⁺ into the perovskite B-site and increased rate of bulk diffusion relative to undoped PIN-PZN-PT. Incorporation of Zn²⁺ into the perovskite lattice increased the tetragonal character of PIN-PZN-PT as demonstrated by tetragonal peak splitting and increased Curie temperature. Sintering in flowing oxygen reduced the solubility of Zn²⁺ in the perovskite lattice and resulted in rhombohedral PIN-PZN-PT. Sintering in oxygen prevented secondary phase formation which resulted in a high-piezoelectric coefficient (d₃₃ – 550 pC/N), high-coercive field (E_c – 13 kV/cm), and high-rhombohedral to tetragonal phase transition temperature (T_r-t – 165°C). We conclude that ZnO-doped PIN-PZN-PT ceramics are excellent candidates for high-power transducer applications.