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

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

Temperature dependent switching mechanism of (Pb[sub 0.92]La[sub 0.08])(Zr[sub 0.65]Ti[sub 0.35])O[sub 3] investigated by small and large signal measurements

The transition region between the field induced ferroelectric and the ergodic phase in relaxor ferroelectrics offers the possibility to study the switching behavior as a function of the increasing relaxor character of the system. Here, field dependent small and large signal measurements are presented. The results obtained at distinct temperatures below the transition temperature Tt for (Pb0.92La0.08)(Zr0.65Ti0.35)O3 concerning P(E), S(E), ϵ33(E), and d33(E) display a strong temperature dependence. Analysis of the reversible and irreversible domain processes leads to the conclusion that switching occurs through an intermediate nanodomain state even in the ferroelectric regime

Light-induced absorption in lead lanthanum zirconate titanate ceramics

Transient light-induced absorption in the near infrared (IR) and visible (vis) spectral range is observed in transparent lanthanum-modified lead zirconate titante piezoelectric ceramics by means of a pump-and-probe-type experiment after pulsed illumination with 532 nm. Its temporal behavior in the IR range is satisfactorily described by a single stretched exponential function, whereas in the vis range a sum of two stretched exponential functions is necessary. The results prove the existence of at least two defect levels in the energetic band gap

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

Relaxor Characteristics of Morphotropic Phase Boundary (Bi1/2Na1/2)TiO3-(Bi1/2K1/2)TiO3 Modified with Bi(Zn1/2Ti1/2)O3

Morphotropic phase boundary (Bi1/2Na1/2)TiO3(Bi1/2K1/2)TiO3 (BNTBKT), was modified with increasing additions of Bi(Zn1/2Ti1/2)O3 (BZT). Microstructure, electric-field-induced strain and polarization, dielectric permittivity, and temperature-dependent piezoelectric coefficient were investigated and compared with crystal structure measured in situ as a function of applied electric field. Furthermore, permittivity and piezoelectric coefficient were characterized as a function of electric field. For small additions of BZT, an applied electric field leads to an irreversible phase transition into a ferroelectric phase with remanent polarization and a reduced relative permittivity. Increasing the content of BZT increased the threshold field for the transition. For additions of more than 2 mol% BZT, the piezoelectric coefficient dropped, permittivity remained almost constant, and a high normalized strain of up to 500 pm/V was observed. However, no field-dependent structural change was evidenced by the in situ X-ray experiment.close373

Capacitance Enhancement of Doped Barium Titanate Dielectrics and Multilayer Ceramic Capacitors by a Post-Sintering Thermo-Mechanical Treatment

High capacitance of miniaturized multilayer ceramic capacitors (MLCCs) is of great interest from both academic and industrial points of view. Because of the limited number of suitable materials (possessing high permittivity and low losses), the capacitance of MLCCs may be enhanced by modifying the capacitor geometry (i.e., by reducing the layer thicknesses or increasing the internal electrodes‧ area) and by optimizing the thermal schedule during processing. In this study, we describe a post-sintering thermo-mechanical treatment to increase the capacitance of dielectrics and MLCCs. A uniaxial mechanical load was applied during the cooling from either below or above the Curie temperature to room temperature. After load release, the permittivity permanently increased at room temperature by ~8%–11% after a stress of 20 MPa had been applied. The configuration of the ferroelectric domains and the residual stress may be responsible for this improvement

High-Frequency EPR Analysis of MnO2-Doped [Bi0.5Na0.5]TiO3-BaTiO3 Piezoelectric Ceramics - Manganese Oxidation States and Materials 'Hardening'

High-frequency electron paramagnetic resonance (EPR) has been used to identify different manganese oxidation states in the 0.5 mol% MnO2-doped (100-x)Bi0.5Na0.5TiO3-xBaTiO(3) (BNT-xBT) solid solution with x = 6. The as-sintered and air-annealed samples show two distinct EPR resonances that were assigned to Mn2+- and Mn3+ -ions, respectively, incorporated at the Ti-site. The equilibrium between acceptor-type Mn ''(Ti)- and Mn'(Ti)-states can be explained by the thermodynamic equilibration under air at the sintering temperature corresponding to [n] > [p], which yields an n-type Mn:BNT-6BT compound.close2

Processing and properties of Na0.5Bi0.5TiO3 piezoelectric ceramics modified with La, Mn AND Fe

Although a great deal of work has been done to understand defect chemistry in "soft" and "hard" PZT-based materials, there is little understanding of how defect chemistry influences the properties of lead-free piezoelectric materials. This paper reports a systematic investigation of doping on the ferroelectric and piezoelectric properties in Na0.5Bi0.5TiO3 (NBT)-based ceramics. NBT-based ceramics have been synthesized by traditional solid state routes using several different dopants including lanthanum, manganese, and iron in 1 mol%. The addition of iron and manganese lead to an increase in the coercive field (Ec), a decrease in the piezoelectric coefficient (d33), and an increase in the thermal depoling temperature (Tdepole), similar to the behavior of "hard" PZT. Lanthanum, on the other hand, leads to a decrease in the Ec, an increase in d33, and a decrease in Tdepole similar to that seen in "soft" PZT