Defect-Accommodating Intermediates Yield Selective Low-Temperature Synthesis of YMnO₃ Polymorphs

Area of Science:

• Materials Science
• Solid-State Chemistry
• Inorganic Synthesis

Background:

• Solid-state metathesis is a low-temperature synthesis route for complex oxides.
• Understanding precursor structure influence is crucial for solid-state synthesis control.
• Yttrium manganese oxides (YMnO3) exist in hexagonal and orthorhombic polymorphs.

Purpose of the Study:

• Investigate the role of precursor structure in solid-state metathesis for YMnO3 synthesis.
• Identify reaction intermediates and temperature regimes leading to hexagonal and orthorhombic YMnO3.
• Explore strategies for selective synthesis of complex oxides via precursor control.

Main Methods:

• Ternary metathesis reaction: LiMnO2 + YOCl → YMnO3 + LiCl.
• Utilized three different LiMnO2 precursors.
• Employed temperature-dependent synchrotron X-ray and neutron diffraction.
• Performed density functional theory (DFT) calculations.

Main Results:

• Identified manganese intermediates undergoing charge disproportionation into tetragonal (Mn(II,III)) and cubic (Mn(III,IV)) spinels.
• Tetragonal spinel leads to hexagonal YMnO3; cubic spinel leads to orthorhombic YMnO3.
• DFT calculations show cation vacancies (∼2.2%) stabilize the orthorhombic YMnO3 polymorph.
• Orthorhombic YMnO3 is the majority product below 600 °C after 2 weeks, indicating defect equilibration.

Conclusions:

• Precursor structure significantly impacts product selectivity in solid-state metathesis.
• Controlling defect-accommodating intermediates offers new low-temperature synthesis strategies.
• This work provides insights into selective synthesis of complex oxides.