Structural phase transitions and switchable dielectric constants of two ionic co-crystals (am)3[La(NO3)6] (am = (n-Pr)3NH, (n-Bu)3NH)

Abstract The reaction of La(NO 3 ) 3 ·6H 2 O and [( n -Pr) 3 NH](NO 3 ) or [( n -Bu) 3 NH](NO 3 ) afforded two ionic co-crystal compounds, namely [( n -Pr) 3 NH] 3 [La(NO 3 ) 6 ] and [( n -Bu) 3 NH] 3 [La(NO 3 ) 6 ], respectively. Both compounds show switchable dielectric behaviors above room temperature, owing to their reversible structural phase transitions confirmed by DSC measurement and variable-temperature powder X-ray diffraction. The former compound can function as a thermosensitive dielectric material over a wide temperature range above room temperature, while the latter may act as a bistable dielectric material with a large e′– T hysteresis loop. The synthetic approach affords an effective strategy to construct switchable dielectric phase transition materials based on large ammonium and lanthanide complex anion.