posted on 2024-01-09, 17:12authored byKunpot Mopoung, Anna Dávid, Xianjie Liu, Mats Fahlman, Irina A. Buyanova, Weimin M. Chen, Yuttapoom Puttisong
We provide direct
evidence for a spin-active V4+ defect
center, likely in the form of a VO2+ complex, predominantly
introduced in single crystals of vanadium-doped Cs2NaInCl6 halide double perovskites grown by the solution-processed
hydrothermal method. The defect has C4v point group symmetry, exhibiting an electron paramagnetic
resonance (EPR) spectrum arising from an effective electron spin of S = 1/2 and a nuclear spin of I = 7/2 (corresponding
to 51V with nearly 100% natural abundance). The determined
electron g-factor and hyperfine parameter values
are g⊥= 1.973, g∥ = 1.945, A⊥ = 180 MHz, and A∥ = 504 MHz,
with the principal axis z along a ⟨001⟩
crystallographic axis. The controlled growth of V-doped Cs2NaInCl6 in an oxygen-free environment is shown to suppress
the V4+ EPR signal. The defect model is suggested to have
a VOCl5 octahedral coordination, where one of the nearest-neighbor
Cl– of V is replaced by O2–, with
octahedral compression along the V–O axis. This VO complex
formation competes with the isolated V3+ substitution of
In3+, which in turn provides a means for the charge-state
tuning of V ions. This finding calls for a better understanding and
control of defect formation in solution-grown halide double perovskites,
which is critical for optimizing and tailoring material design for
solution-processable optoelectronics and spintronics.