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

Peculiar Bi-ion dynamics in Na1/2Bi1/2TiO3 from terahertz and microwave dielectric spectroscopy

Dynamics of the main dielectric anomaly in Na1/2Bi1/2TiO3 (NBT) was studied by time-domain THz and microwave spectroscopy, using also previously published data and their new overall fits. Above the dielectric maximum temperature Tm ~ 600 K, the response consists of coupled sub-THz oscillator and a relaxation mode, assigned to strongly anharmonic Bi-ion vibrations and hopping, whose slowing down explains the paraelectric-like permittivity increase to Tm. Below Tm, the main relaxation continues slowing down and additional relaxation, assigned to quasi-Debye losses, appears in the 10^11 Hz range. The oscillator hardens on cooling and takes over the whole oscillator strength. The permittivity decrease below Tm is caused by the reduced strength of the relaxations due to dominance of the rhombohedral phase within the coexistence region with the tetragonal phase. The anharmonic dynamics of Bi is supported by previous structural studies. NBT represents a hybrid between standard and relaxor ferroelectric behaviour

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

Crack growth resistance (R-curve) behaviour and thermo-physical properties of Al2O3Al_2O_3 particle-reinforced AlN/Al matrix composites

Crack growth resistance behaviour and thermo-physical properties of $Al_2O_3$ particle-reinforced AlN/Al matrix composites have been studied as a function of AlN volume fraction as well as $Al_2O_3$ particle size. The fracture toughness of the composites decreased with increase in vol% AlN and decrease in $Al_2O_3$ particle size. All the composites exhibited R-curve behaviour which has been attributed to crack bridging by the intact metal ligaments behind the crack tip. The Young’s modulus of the composites increased with the vol% of AlN whereas the thermal diffusivity and coefficient of thermal expansion followed a reverse trend. The composites exhibited hysteresis in thermal expansion as a function of temperature and the hysteresis decreased with decrease in metal content of the composite

Crack growth resistance (R-curve) behaviour and thermo-physical properties of Al<SUB>2</SUB>O<SUB>3</SUB> particle-reinforced AlN/Al matrix composites

Crack growth resistance behaviour and thermo-physical properties of Al2O3 particle-reinforced AlN/Al matrix composites have been studied as a function of AlN volume fraction as well as Al2O3 particle size. The fracture toughness of the composites decreased with increase in vol% AlN and decrease in Al2O3 particle size. All the composites exhibited R-curve behaviour which has been attributed to crack bridging by the intact metal ligaments behind the crack tip. The Young's modulus of the composites increased with the vol% of AlN whereas the thermal diffusivity and coefficient of thermal expansion followed a reverse trend. The composites exhibited hysteresis in thermal expansion as a function of temperature and the hysteresis decreased with decrease in metal content of the composite

Role of (Bi1/2K1/2)TiO3 in the dielectric relaxations of BiFeO3-(Bi1/2K1/2)TiO3 ceramics

Temperature-dependent dielectric relaxations of (1 - x)BiFeO3-x(Bi1/2K1/2)TiO3 (BF-BKT) lead-free piezoceramics (0.4 ??? x ??? 0.8) were investigated via impedance spectroscopic techniques. Regardless of the compositions, the dielectric maximum temperatures exhibit a frequency-dependent dispersion, originating from a Debye relaxation due to the presence of oxygen vacancies. It was also observed that there exist local dielectric maxima due to the relaxation of polar nanoregions as a shoulder on the lower temperature side. The onset temperature for the Debye-type relaxation decreased with decreasing BKT content, gradually overlapping with the low-temperature dielectric dispersion from the relaxation of polar nanoregions. It is proposed that the role of BKT in the BF-BKT system is to enhance the random fields that favor a relaxor state and to suppress the Debye-type relaxation of oxygen vacancy related dipoles.clos

Hardening behavior and highly enhanced mechanical quality factor in (K0.5Na0.5)NbO3-based ceramics

This paper relates the microstructure, crystallographic structure, ferroelectric, and piezoelectric properties of (K0.5Na0.5)NbO3 (KNN) ceramics modified with 0.38mol% K5.4Cu1.3Ta10O29 (KCT) and different amounts of CuO. Results revealed that the addition of KCT and CuO were effective in enhancing the sinterability of KNN. The internal bias field (E ib) increased from 0.3kV/mm to 0.58kV/mm at 0.5mol% CuO-added KNN+KCT ceramics. The increase of E ib corresponds very well with the observed increase of the mechanical quality factor (Q m) from 112 to 2665 for 0.5mol% CuO. Besides, addition of 0.5mol% CuO to KNN+KCT resulted in a large increase of the EPR signal, which is related to the increased amount Cu2+ and a corresponding increase of the concentration of defect dipoles. This result is in good agreement with the increased E ib and the resulting hardening behavior.clos