Achieving excellent temperature-stable dielectric properties of Bi_(0.5)Na_(0.5)TiO_(3)-based lead-free ceramics via doping AgNbO_(3)

The lead-free ceramics(1−x)(0.94Bi0.47Na0.47Ba0.06TiO3-0.06BiAlO3)-xAgNbO3(denoted as BNBTA-xAN)were synthesized via a solid-state sintering method.The effect of AgNbO3 doping amount on dielectric properties of the ceramics was studied systematically.X-ray diffraction(XRD),scanning electron microscope(SEM)and Raman spectroscope were used to detect the structure of the ceramics.Temperature-dependent dielectric spectra,frequency-dependent dielectric constant and alternating current(ac)electric conductance at various temperatures were measured.The doping of AgNbO3 greatly reduces dielectric constant around Curie temperature and thus enhances the temperature stability of the dielectric constant.The ceramic BNBTA-0.03AN exhibits excellent temperature-stable dielectric properties with temperature coefficient of capacitance(TCC)≤±15%between 55°C and 418°C with temperature window 363°C and small changes of dielectric constant and dielectric loss from 100 Hz to 1 MHz at different temperatures.The obtained ceramics are expected to be used in high-temperature capacitors due to its excellent temperature stability.

Improved ferroelectric and piezoelectric properties of(Na_(0.5)K_(0.5))NbO_(3)ceramics via sintering in low oxygen partial pressure atmosphere and adding LiF

Dense(Na_(0.5)K_(0.5))NbO_(3)lead-free ceramics with the simple composition were prepared via sintering in low oxygen partial pressure(pO_(2),~10^(−12) atm)atmosphere and adding LiF.All the ceramics have pure orthorhombic structure.Compared to the LiF-added(Na_(0.5)K_(0.5))NbO_(3)ceramics sintered in air and the low pO_(2)-sintered pure(Na_(0.5)K_(0.5))NbO_(3)ceramics without LiF addition,the present ceramics exhibit improved piezoelectric and ferroelectric properties.The piezoelectric constant d33 is 125 pC/N,and the converse piezoelectric constant d_(33)^(*)is 186 pm/V.The dielectric constant and dielectric loss of the ceramics at room temperature and 1 kHz are 451 and 0.03,respectively.Under the measured electric field of 70 kV/cm,the remanent polarization is 25.9μC/cm^(2)and the coercive field is 13.9 kV/cm.Furthermore,if the base metals such as Cu and Ni powders were mixed into the green pellets and sintered in the low pO_(2)atmosphere,the base metals cannot be oxidized,suggesting possibility of using base metals as electrodes.