Linear and nonlinear dielectric spectroscopy in dipolar glasses

Abstract

Two dipolar glass systems are investigated by broadband dielectric spectroscopy. The two systems under investigation, NH.I:KI and solid solutions of deuterated betaine phosphate and betaine phosphite (BP BPI), reveal very different freezing scenarios. The dielectric loss in NH.IKI is characterized by a powerlaw behavior on frequency &" -Y', indicative for the nearequilibrium dynamics in the glass phase. The deuterated proton glass D-BPBPI (40:60) exhibits a relaxational-type of freezing transition. Measurements of the nonlinear susceptibility and of the field cooled and zero-field cooled susceptibility provide clear evidence for a "static" dipolar glass transition at T, -28 K ? 2 K.

Suppression of phase transitions and glass phase signatures in mixed cation halide perovskites

“…Further support for the emergence of a glassy phase is provided by the evolution of the dielectric curves throughout the frequency and temperature range investigated. Such behavior is typically observed for other dipolar glasses 45,46,58 . Note that the increase of ε* observed at low frequencies for all compounds is not related to the molecular dynamics, but instead occurs due to the conductivity effects 59 .…”

“…Dielectric anomalies associated with these phases are usually very broad with respect to both frequency and temperature. In addition, at sufficiently low temperature, a freezing of the electric dipoles may occur with dynamics described by the Vogel-Fulcher law instead of the typical Arrhenius behavior 43,46,47 .…”

Mixology of MA1-xEAxPbI3 Hybrid Perovskites: Phase Transitions, Cation Dynamics and Photoluminescence

“…Such a broad dipolar relaxation of the highly mixed compounds may indicate that the MA cations form a dipolar glass phase due to the dipole frustration introduced by mixing, which is frequently observed in mixed inorganic compounds. [66][67][68][69] However, here we did not observe a clear Vogel-Fulcher behaviour of the mean relaxation time despite our broadband (Hz-GHz) approach, as the Arrhenius law was sufficient to describe the obtained data (Figure S13). Observation of the Vogel-Fulcher law would indicate freezing of the electric dipoles and would provide an unequivocal evidence of such a phase formation.…”

“…Observation of the Vogel-Fulcher law would indicate freezing of the electric dipoles and would provide an unequivocal evidence of such a phase formation. 67,68 The absence of this behaviour suggests that the freezing might occur at very low temperatures. Note that similar hints to the glassy phase formation were also observed in the dielectric responses of the related MA 1-x DMA x PbBr 3 (strong signatures) 32 and MA 1-x FA x PbBr 3 (weaker signatures) 39 systems.…”

Mixology of MA1–xEAxPbI3 Hybrid Perovskites: Phase Transitions, Cation Dynamics, and Photoluminescence

“…Such a broad dipolar relaxation of the highly mixed compounds may indicate that the MA cations form a dipolar glass phase due to the dipole frustration introduced by mixing, which is frequently observed in mixed inorganic compounds. − However, here, we did not observe a clear Vogel–Fulcher behavior of the mean relaxation time despite our broad-band (Hz–GHz) approach, as the Arrhenius law is sufficient to describe the obtained data (Figure S13). Observation of the Vogel–Fulcher law would indicate freezing of the electric dipoles and would provide an unequivocal evidence of such phase formation. , The absence of this behavior suggests that the freezing might occur at very low temperatures. Note that similar hints to the glassy phase formation were also observed in the dielectric responses of the related MA 1– x DMA x PbBr 3 (strong signatures) and MA 1– x FA x PbBr 3 (weaker signatures) systems.…”