Suppression of Phase Transition and Dipolar Glassy Behavior in Dimethylammonium/Methylammonium Lead Chloride Single Crystals

The A-site doping in ABX3 perovskite structures has been demonstrated to effectively enhance the structural properties of these materials by influencing their phase transitions. In this study, we systematically investigate the structural, vibrational, and dielectric properties of DMAxMA1–xPbCl3 (0 ≤ x ≤ 0.494) mixed halide perovskite single crystals, emphasizing the role of DMA substitution in altering crystal symmetry, phase transitions, and dipolar dynamics. Comprehensive structural analysis via powder X-ray diffraction and Raman spectroscopy confirms the successful incorporation of DMA into the perovskite lattice, maintaining a high-quality cubic phase at room temperature without secondary phases. Increasing DMA concentration induces gradual lattice expansion and structural distortion, attributed to substitutional effects. Notably, NMR spectroscopy reveals that the actual DMA incorporation surpasses the nominal synthesis range (0 ≤ x ≤ 0.25), reaching up to x = 0.494, likely due to precursor solubility and reactivity differences. Temperature-dependent Raman and Brillouin spectroscopy unveil a structural phase transition from cubic to orthorhombic symmetry at low DMA concentrations (0.072 ≤ x ≤ 0.237), while at higher concentrations (x = 0.312, 0.494), the cubic phase remains fully stabilized with no detectable transitions. XRD, heat capacity, and dielectric spectroscopy further demonstrate that increased DMA incorporation induces structural disorder and dielectric broadening, indicative of dipolar glassy behavior. Notably, Vogel–Fulcher analysis of dielectric relaxation for x = 0.494 reveals cation freezing at 108 K, alongside low Debye and Einstein temperatures, suggesting pronounced lattice softness. These findings contribute to a deeper understanding of A-site cation substitution and its influence on phase stability and dielectric properties. The observed correlations between crystal symmetry, structural disorder, and dipolar dynamics provide valuable insights for the development of perovskite materials with controlled phase transition characteristics for specific applications.