Abstract
In this paper, the structural and dielectric properties of BNO (BiNbO4)
was investigated as a function of the external RF frequency and
temperature. The BNO Ceramics, prepared by the conventional mixed oxide
method and doped with 3, 5 and 10 wt. % Bi2O3-PbO were sintered at
1,025 A degrees C for 3 h. The X-ray diffraction patterns of the samples
sintered, shown the presence of the triclinic phase (beta-BNO). In the
measurements obtained at room temperature (25 A degrees C) was observed
that the largest values of dielectric permittivity (epsilon' (r) ) at
frequency 100 kHz, were for the samples: BNO5Bi (5 wt. % Bi2O3) and
BNO5Pb (5 wt. % PbO) with values epsilon' (r) similar to 59.54 and
epsilon' (r) similar to 78.44, respectively. The smaller values of loss
tangent (tan delta) were for the samples: BNO5Bi and BNO3Pb (3 wt. %
PbO) with values tan delta similar to 5.71 x 10(-4) and tan delta
similar to 2.19 x 10(-4), respectively at frequency 33.69 MHz. The
analysis as a function of temperature of the dielectric properties of
the samples, obtained at frequency 100 kHz, showed that the larger value
of the relative dielectric permittivity was about epsilon' (r) similar
to 76.4 at temperature 200 A degrees C for BNO5Pb sample, and the value
smaller observed of dielectric loss was for BNO3Bi sample at temperature
80 A degrees C, with about tan delta similar to 5.4 x 10(-3). The
Temperature Coefficient of Capacitance (TCC) values at 1 MHz frequency,
present a change of the signal from BNO (-55.06 ppm/A degrees C) to the
sample doped of Bi: BNO3Bi (+86.74 ppm/A degrees C) and to the sample
doped of Pb: BNO3Pb (+208.87 ppm/A degrees C). One can conclude that
starting from the BNO one can increase the doping level of Bi or Pb and find a concentration where one have TCC = 0 ppm/A degrees C, which is
important for temperature stable materials applications like high
frequency capacitors. The activation energy (H) obtained in the process
is approximately 0.55 eV for BNO sample and increase with the doping
level. These samples will be studied seeking the development ceramic
capacitors for applications in radio frequency devices.
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