Piezoelectric properties of unmodified and La-modified NBT. (a)Polarization and (b) strain measurements as a function of applied electric field at a frequency of 1 Hz on unmodified and La-modified NBT.
The thermal depolarization of NBT, as measured via the (a) in situ converse, and (b) ex situ direct piezoelectric coefficients. The temperatures shown in part b are the annealing temperatures.
Relative permittivity and tan δ at selected frequencies and temperature for poled samples of (a) unmodified, (b) 0.5 at. % La-modified, (c) 1.0 at. % La-modified, and (d) 1.5 at. % La-modified NBT.
Selected portions of HR-XRD patterns of NBT with varying La substitution. For simplicity, diffraction profiles are labeled relative to the pseudo-cubic planes.
Rietveld refinement of an HR-XRD pattern of 1 at. % La-modified NBT showing the observed pattern (x) and the calculated fit (—). The line beneath is the difference between the observed and calculated intensities.
Selected portions of HR-XRD patterns of 1 at. % La-substituted NBT at select temperatures.
Selected portions of HR-XRD patterns of (a) unmodified and (b) 1 at. % La substituted NBT as a function of temperature.
Coercive field of the various La-modified NBT compositions is shown versus the c/b lattice parameter ratio (right) and the β/βpc angle ratio (left). The βpc is the monoclinic angle for a cubic unit cell represented using a monoclinic setting.
Depolarization temperature determined from measurements of in situ converse d 33 of the various La-modified NBT compositions is shown versus the calculated Pm m phase fraction at room temperature (bottom) and at 250 °C (top).
Depolarization temperatures, Td (°C), measured by in situ converse d 33, ex situ direct d 33 and permittivity in all investigated compositions.
Refined phase fractions, lattice parameters, cell volume, and criteria of fit parameters for samples with increasing La concentration at room temperature.
Refined phase fractions, lattice parameters, cell volume, and criteria of fit parameters for the 1 at. % La substituted NBT at selected temperatures.
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