Unveiling the Monoclinic Phase in CsPbBr_3-Cl Perovskite Crystals, Phase Transition Suppression and High Energy...

Area of Science:

• Materials Science
• Crystallography
• Solid-State Physics
• Nuclear Instrumentation

Background:

• All-inorganic cesium lead halide perovskites (CsPbX₃) are promising for solar cells and radiation detection due to their stability.
• Previous studies identified specific crystal structures and phase transition behaviors for these materials.

Purpose of the Study:

• To investigate the crystallographic properties and phase transition behaviors of CsPbBr_3-xCl_x (x = 0-3) solid solutions.
• To evaluate the performance of CsPbBr₂Cl single crystals as γ-ray detectors.

Main Methods:

• Single crystal growth using the Bridgman method.
• Extensive crystallographic analysis (including X-ray diffraction) on 7 different compositions.
• Fabrication and characterization of γ-ray detectors using CsPbBr₂Cl crystals.
• Thermally stimulated current spectroscopy to assess defect densities.

Main Results:

• CsPbBr_3-xCl_x crystals exhibit eutectoid behavior in melting points and phase transition temperatures.
• A phase transition temperature near room temperature was observed for CsPbBr₂Cl (∼37 °C).
• Contrary to prior beliefs, CsPbBr₃ and CsPbCl₃ exhibit a monoclinic structure (space group P2₁/m) at room temperature, not orthorhombic (Pnma).
• The new structural model has a unit cell volume four times larger than the previously accepted orthorhombic model.
• CsPbBr₂Cl γ-ray detectors achieved an energy resolution of 7.2% at 200 V for ⁵⁷Co radiation.
• Low and uniform defect densities (∼4.72-5.09 × 10¹² cm^-3) were found in CsPbBr₂Cl crystals.

Conclusions:

• The study reveals a novel monoclinic crystal structure for CsPbBr₃ and CsPbCl₃ at room temperature, refining previous structural assignments.
• The demonstrated performance of CsPbBr₂Cl as a γ-ray detector, attributed to its low defect density, highlights its potential for radiation detection technologies.