Two-Step Structure Phase Transition, Dielectric Anomalies, and Thermochromic Luminescence Behavior in a Direct Band Gap 2D Corrugated Layer Lead Chloride Hybrid of [(CH3)4N]4Pb3Cl10

A direct band gap 2D corrugated layer lead chloride hybrid, [(CH3)(4)N](4)Pb3Cl10 (1), shows analogous topology to the {Mg3F104-} layer in Cs4Mg3F10, and with the (CH3)(4)N+ cations locating in the inorganic layer voids and between the interlayers. Two reversible structural phase transitions occur in 1 at 225/210K and 328/325K upon heating/cooling, respectively. On going from the low- to intermediate-temperature phase, the space group changes from P2(1)/c to Cmca, and the crystallographic axis perpendicular to the layers is doubled with the order-disorder transformation of (CH3)(4)N+ cations between the interlayers. The intermediate- and high-temperature phases are isomorphic with similar cell parameters and packing structure; their main difference concerns the disorder degree of the (CH3)(4)N+ cations between the interlayers. The two-step structural phase transitions lead to dielectric anomalies around the corresponding T-c. Interestingly, 1 shows multiband emission, originating from the recombination of exciton and emission of defects. Moreover, 1 exhibits divergent thermochromic luminescent features around the T-c on the intermediate to low temperature transition.