Influence of electric fields on the depolarization temperature of Mn-doped (1-x)Bi1/2Na1/2TiO3-xBaTiO(3)

The transition between induced long-range order and relaxor-like behavior upon heating is investigated in lead-free (1-x)Bi1/2Na1/2(Ti0.995Mn0.005)O-3-xBa(Ti0.995Mn0.005)O-3 piezoceramics with x = 0.03, 0.06, and 0.09 (BNT-100xBT:Mn). Temperature-dependent permittivity epsilon'(T) and thermally stimulated depolarization currents (TSDC) of poled samples were measured under identical heating conditions to clarify the depolarization mechanism. In both methods, the influence of electric bias fields on the transition temperature was investigated. Fields applied in the poling direction shift the transition to higher temperatures, with corresponding results in epsilon'(T) and TSDC measurements. While the response of transition temperature to external fields displays a similar trend in all investigated compositions, the shape of TSDC is clearly connected with the composition and, hence, the crystal symmetry of the sample. Furthermore, the comparison of epsilon'(T) and TSDC data reveals a systematic shift between transition temperatures obtained with the two different methods.open322

Electric-field-temperature phase diagram of the ferroelectric relaxor system (1-x)Bi1/2Na1/2TiO3-xBaTiO3 doped with manganese

The electric-field-temperature phase diagram for the lead-free relaxor material (1 - x)(Bi1/2Na1/2)TiO3 - xBaTiO 3 (x = 0.03, 0.06, and 0.09) doped with 0.5 mol% Mn (BNT-100xBT:Mn) was established. Transition lines between ergodic or nonergodic relaxor states and the field-induced ferroelectric state were determined at constant temperatures with electric-field-dependent measurements of the polarization as well as of the piezoelectric coefficient and permittivity. Near the depolarization temperature Td, the switching between two ferroelectric poling directions occurs in two steps via an intermediate relaxor state. This effect is closely related to the pinching of the ferroelectric hysteresis loop.open2

Nanoscale phase quantification in lead-free (Bi1/2Na1/2)TiO3-BaTiO3 relaxor ferroelectrics by means of Na 23 NMR

We address the unsolved question on the structure of relaxor ferroelectrics at the atomic level by characterizing lead-free piezoceramic solid solutions (100-x)(Bi1/2Na1/2)TiO3-xBaTiO3 (BNT-xBT) (for x=1,4,6, and 15). Based on the relative intensity between spectral components in quadrupolar perturbed Na23 nuclear magnetic resonance, we present direct evidence of the coexistence of cubic and polar local symmetries in these relaxor ferroelectrics. In addition, we demonstrate how the cubic phase vanishes whenever a ferroelectric state is induced, either by field cooling or changing the dopant amount, supporting the relation between this cubic phase and the relaxor state.open0

Unexpectedly high piezoelectricity of Sm-doped lead zirconate titanate in the Curie point region

Large piezoelectric coefficients in polycrystalline lead zirconate titanate (PZT) are traditionally achieved through compositional design using a combination of chemical substitution with a donor dopant and adjustment of the zirconium to titanium compositional ratio to meet the morphotropic phase boundary (MPB). In this work, a different route to large piezoelectricity is demonstrated. Results reveal unexpectedly high piezoelectric coefficients at elevated temperatures and compositions far from the MPB. At temperatures near the Curie point, doping with 2 at% Sm results in exceptionally large piezoelectric coefficients of up to 915 pm/V. This value is approximately twice those of other donor dopants (e.g., 477 pm/V for Nb and 435 pm/V for La). Structural changes during the phase transitions of Sm-doped PZT show a pseudo-cubic phase forming ≈50 °C below the Curie temperature. Possible origins of these effects are discussed and the high piezoelectricity is posited to be due to extrinsic effects. The enhancement of the mechanism at elevated temperatures is attributed to the coexistence of tetragonal and pseudo-cubic phases, which enables strain accommodation during electromechanical deformation and interphase boundary motion. This work provides insight into possible routes for designing high performance piezoelectrics which are alternatives to traditional methods relying on MPB compositions

On the phase identity and its thermal evolution of lead free (Bi1/2Na1/2)TiO3-6 mol% BaTiO3

Temperature-dependent dielectric permittivity of 0.94(Bi1/2Na1/2) TiO3-0.06BaTiO(3) (BNT-6BT) lead-free piezoceramics was studied to disentangle the existing unclear issues over the crystallographic aspects and phase stability of the system. Application of existing phenomenological relaxor models enabled the relaxor contribution to the entire dielectric permittivity spectra to be deconvoluted. The deconvoluted data in comparison with the temperature-dependent dielectric permittivity of a classical perovskite relaxor, La-modified lead zirconate titanate, clearly suggest that BNT-6BT belongs to the same relaxor category, which was also confirmed by a comparative study on the temperature-dependent polarization hysteresis loops of both materials. Based on these results, we propose that the low-temperature dielectric anomaly does not involve any phase transition such as ferroelectric-toantiferroelectric. Supported by transmission electron microscopy and X-ray diffraction experiments at ambient temperature, we propose that the commonly observed two dielectric anomalies are attributed to thermal evolution of ferroelectric polar nanoregions of R3c and P4bm symmetry, which coexist nearly throughout the entire temperature range and reversibly transform into each other with temperature.open1128

Influence of electric fields on the depolarization temperature of Mn-doped (1-x)Bi1/2Na1/2TiO3-xBaTiO3

The transition between induced long-range order and relaxor-like behavior upon heating is investigated in lead-free (1-x)Bi1/2Na1/2(Ti0.995Mn0.005)O3-xBa(Ti0.995Mn0.005)O3 piezoceramics with x¼0.03, 0.06, and 0.09 (BNT-100xBT:Mn). Temperature-dependent permittivity e0(T) and thermally stimulated depolarization currents (TSDC) of poled samples were measured under identical heating conditions to clarify the depolarization mechanism. In both methods, the influence of electric bias fields on the transition temperature was investigated. Fields applied in the poling direction shift the transition to higher temperatures, with corresponding results in e0(T) and TSDC measurements. While the response of transition temperature to external fields displays a similar trend in all investigated compositions, the shape of TSDC is clearly connected with the composition and, hence, the crystal symmetry of the sample. Furthermore, the comparison of e0(T) and TSDC data reveals a systematic shift between transition temperatures obtained with the two different methods

Thermal Depolarization in the High-Temperature Ternary Piezoelectric SystemxPbTiO3-yBiScO3-zBi(Ni1/2Ti1/2)O3

In the high-temperature ternary perovskite piezoelectric system xPbTiO3–yBiScO3–zBi(Ni1/2,Ti1/2)O3 (PT–BS–BNiT), the addition of bismuth to the A site and nickel to the B site leads to compositions that exhibit diffuse relaxor-like behavior. For these, depolarization temperature, not Curie point, is the critical value of temperature. Depolarization temperature (Td) is defined as the temperature at which the steepest loss in polarization occurs. This temperature is observed in poled materials through two different methods: loss tangent measurements and in situ d33. Across the ternary system, multiple dielectric anomalies occurred which was observed in dielectric tests where the dielectric peak broadens and becomes frequency dependent as BNiT content increased. For different compositions, the value of Td ranged between 275°C–375°C. Values for the piezoelectric coefficient increased with temperature up to d33 = 1000 pC/N during in situ d33. High temperature (up to 190°C) and high field (up to 40 kV/cm) were also applied to test ferroelectric properties in these regimes

Cycling stability of lead-free BNT-8BT and BNT-6BT-3KNN multilayer actuators and bulk ceramics

his study presents the electromechanical properties and cycling stability of lead-free piezoelectric materials 0.92(Bi1/2Na1/2)TiO3-0.08BaTiO(3) (BNT-8BT) and 0.91(Bi1/2Na1/2)TiO3-0.06BaTiO(3)-0.03(K0.5Na0.5)NbO3 (BNT-6BT-3KNN). Both bulk samples as well as multilayer actuators (MLA) with internal Ag/Pd (70/30) electrodes were successfully processed from both materials. Electromechanical characteristics in the non-fatigued state and after different numbers of unipolar fatigue cycles are provided, representing the first direct comparison of the fatigue resistance of lead-free bulk ceramics and the corresponding MLAs. At a maximum field of 6 kV/mm and a frequency of 50 Hz, BNT-8BT MLA delivered a maximum strain of 0.07% and displayed excellent cycling stability. BNT-6BT-3KNN MLA provided a higher strain of 0.15% initially but degraded during cycling and exhibited break down after 10(7) cycles. Furthermore, the frequency dependence of strain and the self-heating during cycling were investigated. The temperature increase is limited only to 2 degrees C in BNT-8BT MLA and 13 degrees C in BNT-6BT-3KNN MLA.close5

Nanoscale phase quantification in lead-free (Bi1/2Na1/2)TiO₃-BaTiO₃ relaxor ferroelectrics by means of ²³Na NMR

We address the unsolved question on the structure of relaxor ferroelectrics at the atomic level by characterizing lead-free piezoceramic solid solutions (100−x)(Bi1/2Na1/2)TiO₃−xBaTiO₃ (BNT−xBT) (for x=1,4,6, and 15). Based on the relative intensity between spectral components in quadrupolar perturbed ²³Na nuclear magnetic resonance, we present direct evidence of the coexistence of cubic and polar local symmetries in these relaxor ferroelectrics. In addition, we demonstrate how the cubic phase vanishes whenever a ferroelectric state is induced, either by field cooling or changing the dopant amount, supporting the relation between this cubic phase and the relaxor state