Two Polymorphs of BaZn₂P₂: Crystal Structures, Phase Transition, and Transport Properties

Area of Science:

• Solid State Chemistry
• Materials Science
• Crystallography

Background:

• The β-BaZn₂P₂ compound belongs to the ThCr₂Si₂ structure type.
• Structural phase transitions between α-BaCu₂S₂ and ThCr₂Si₂ types are known.
• The existence of distinct structural polymorphs in BaZn₂P₂ was explored.

Purpose of the Study:

• To synthesize and characterize the novel α-BaZn₂P₂ polymorph.
• To investigate the structural phase transition between α- and β-BaZn₂P₂.
• To determine the electronic and transport properties of α-BaZn₂P₂.

Main Methods:

• Single crystal X-ray diffraction for structural elucidation.
• Thermal analysis (Differential Scanning Calorimetry/Thermogravimetric Analysis) for phase transition studies.
• Transport property measurements and band structure calculations.

Main Results:

• The α-BaZn₂P₂ polymorph crystallizes in the orthorhombic α-BaCu₂S₂ structure type.
• A first-order phase transition from the α-phase to the tetragonal β-phase occurs at ~1123 K.
• α-BaZn₂P₂ is a p-type semiconductor with a direct bandgap of 0.5 eV and a Seebeck coefficient of 119 μV/K at room temperature.

Conclusions:

• The synthesis and characterization of α-BaZn₂P₂ provide a new structural polymorph for the BaZn₂P₂ system.
• The observed phase transition highlights the structural versatility of BaZn₂P₂.
• The semiconducting nature and electronic properties of α-BaZn₂P₂ suggest potential applications in electronic devices.