posted on 2023-01-06, 06:03authored byLinyu Bai, Dongjie Liu, Xian Zhao, Fapeng Yu, Yanlu Li
Increasing the crystal resistivity is critically important
for
enhancing the signal-to-noise ratio and improving the sensing capability
of high-temperature piezoelectric sensors based on langasite-type
crystals. The resistivity of structural ordered langasite-type crystals
is much higher compared to that of the disordered crystals. Here,
we selected structural ordered Ca3TaGa3Si2O14 (CTGS) and disordered La3Ga5SiO14 (LGS) as representatives to investigate the
microscopic conduction mechanism and further reveal the origin of
the different resistivities of the ordered and disordered langasite-type
crystals at elevated temperatures. By combining first-principles calculations
and experimental investigations, we found that the different conductivity
behaviors of the ordered and disordered crystals originate from different
types of point defects formed in the crystal and their different contributions
to the conductivity. For the disordered LGS crystal, the oxygen vacancies
are apt to be formed at high temperatures, promoting the transition
of valence electrons and yielding high conductivity. For the ordered
CTGS crystal, the dominant TaGa antisite defects can introduce
an electron–hole recombination center in the electronic band
gap, significantly shortening the carrier lifetime and thus reducing
the conductivity. This provides effective guidance to improve the
resistivity performance of langasite-type crystals at high temperatures
by optimizing the experimental conditions, such as oxygen atmosphere
treatment, antisite defect modification, etc.