Role of NH₄ ions in successive phase transitions of perovskite type (NH₄)₂ZnX₄ (X = Cl, Br) by ¹H MAS NMR and ¹⁴N NMR

Abstract

The 1H chemical shifts and the spin-lattice relaxation time, T1ρ, in the rotating frame of (NH4)2ZnX4 (X = Cl, Br) are observed in order to investigate local phenomena related to successive phase transitions.

Study on Paramagnetic Interactions of (CH3NH3)2CoBr4 Hybrid Perovskites Based on Nuclear Magnetic Resonance (NMR) Relaxation Time

“…From the 13 C T 1ρ curves, the relaxation processes of (CH 3 NH 3 ) 2 CdBr 4 are affected by molecular motion described by the Bloembergen–Purcell–Pound (BPP) theory [22]. The experimental values of T 1ρ are explained by the correlation time τ C for molecular motion based on the BPP theory [22,23], (1/T 1ρ ) = 0.05( μ o /4π) 2 [γ H 2 γ C 2 ħ 2 / r 6 ][4F a + F b + 3F c + 6F d + 6F e ] where F a = τ C /[1 + ω 1 2 τ C 2 ]F b = τ C /[1 + (ω H ‒ ω C ) 2 τ C 2 ]F c = τ C /[1 + ω C 2 τ C 2 ]F d = τ C /[1 + (ω H + ω C ) 2 τ C 2 ]F e = τ C /[1 + ω H 2 τ C 2 ]. where μ o is the permeability, γ H and γ C are the respective gyromagnetic ratios for the 1 H and 13 C nuclei, r is the distance of H–C, ħ = h/2π, and ω H and ω C are the respective Larmor frequencies of 1 H and 13 C.…”