RP was characterized using a Rigaku Smartlab 9 kW diffractometer with
a Cu source to acquire the XRD patterns. The particle size of the
RP was checked with a Malvern Mastersizer 2000 DLS analyzer. The sample
is first dispersed in water using a probe sonicator to destroy aggregates.
The dispersion is then added to the tank of the DLS analyzer, where
a He/Ne laser (633 nm) and a diode laser (466 nm) are both used to
determine the particle-size distribution. Zeiss Merlin SEM was also
used to analyze the particle size. A built-in Oxford Instruments X-Max
150 energy-dispersive X-ray (EDX) was used to analyze the element
distribution in the sample. For the cross-sectional analysis, samples
were cut using a precision etching and coating system II (PECS) Gatan,
using an argon ion beam. JEOL 3000F field emission gun TEM was used
to check the composites. A Renishaw InVia Raman microscope was used
to acquire the Raman spectra, using a 785 nm diode laser.