The
design of nanomaterials by tailoring the size, shape, and surface
chemistry has a significant impact on their properties. The fine-tuning
of structural defects of ceria rod-like and cube-like-shaped nanoparticles
was performed via La3+ doping in molar ratios of 0–70
mol %. Morphology control was achieved by varying the hydrothermal
synthesis temperature. For La
x
Ce1–x
O2–x/2 samples
prepared at 110 °C, nanorod-like structures are obtained for x < 0.30 and a random morphology of interconnecting polyhedra
is achieved for a larger x. The ceria fluorite crystalline
structure is maintained at an x of up to 0.60, and
both Raman and X-ray diffraction results indicate a high level of
defects and disorder in the crystalline structure. For La
x
Ce1–x
O2–x/2 samples prepared at 180 °C, cube-shaped particles
are predominant for an x of up to 0.10; however,
for x
> 0.20, two fluorite phases
with
different lattice parameters are associated with two distinct shapes,
cubes and rods The La concentration in nanocubes is limited to x = 0.10 even for samples prepared with higher nominal La
concentrations, whereas the nanorods contain larger La concentrations.
The demonstrated morphology and defect control on La-doped ceria nanoparticles
are critical for applications such as high-temperature oxide catalysts.
Stability and maintenance of the crystal structure are
the main
drawbacks of the application of organic–inorganic perovskites
in photovoltaic devices. The ΔT = 62 K robust
shift of the structural phase transition observed here allows us to
conduct a comprehensive study at room temperature of the tetragonal versus cubic phase on MAPbI3. The absence of
the shift in the cubic transition for all-inorganic CsPbI3 samples confirms the importance of both orientation and dynamics
of the organic cations. Our results provide a unique opportunity to
evaluate the physical properties of both cubic and tetragonal phases
of MAPbI3 at the same temperature, eliminating different
phonon effects as possible causes for different properties. Besides
higher electrical resistivity, the perovskite cubic phase presents
a faster charge carrier lifetime than the tetragonal phase and partial
PL quenching, pointing toward increased trap-assisted nonradiative
recombination. The light absorption coefficient in the cubic phase
is larger than the absorption in the tetragonal phase in the green
region.
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