jz6b00803_si_003.cif (112.23 kB)
Is CH3NH3PbI3 Polar?
dataset
posted on 2016-06-10, 00:00 authored by Sharada G, Pratibha Mahale, Bhushan
P. Kore, Somdutta Mukherjee, Mysore S. Pavan, Chandan De, Somnath Ghara, A. Sundaresan, Anshu Pandey, Tayur N. Guru
Row, D. D. SarmaIn view of the continued
controversy concerning the polar/nonpolar
nature of the hybrid perovskite system, CH3NH3PbI3, we report the first investigation of a time-resolved
pump–probe measurement of the second harmonic generation efficiency
as well as using its more traditional form as a sensitive probe of
the absence/presence of the center of inversion in the system both
in its excited and ground states, respectively. Our results clearly
show that SHG efficiency, if nonzero, is below the limit of detection,
strongly indicative of a nonpolar or centrosymmetric structure. Our
results on the same samples, based on temperature dependent single
crystal X-ray diffraction and P–E loop measurements, are entirely consistent with the above conclusion
of a centrosymmetric structure for this compound in all three phases,
namely the high temperature cubic phase, the intermediate temperature
tetragonal phase and the low temperature orthorhombic phase. It is
important to note that all our experimental probes are volume averaging
and performed on bulk materials, suggesting that basic material properties
of CH3NH3PbI3 are consistent with
a centrosymmetric, nonpolar structure.