Low-Temperature Synthesis of Magnetic Pyrochlores (R2Mn2O7, R = Y, Ho-Lu) at Ambient Pressure and Potential for High-Entropy Oxide Synthesis

Rare-earth manganese pyrochlores (R2Mn2O7) are frustrated magnetic materials,which previouslyhave only been accessed using expensive high-pressure and high-temperaturesynthesis. In the present work, a series of pyrochlores (R = Y, Ho-Lu)were prepared by a simple and cost-effective molten salt method atambient pressure. The synthetic procedure does not require high pressuresor temperatures nor oxygen flow. The versatility of the method wasconfirmed by the preparation of a mixed rare-earth Y0.4Er0.4Tm0.4Yb0.4Lu0.4Mn2O7 solid solution. Rare-earth manganesepyrochlores (R2Mn2O7) are frustratedmagnetic materials, which previously haveonly been accessed using expensive high-pressure and high-temperaturesynthesis. In the present work, we demonstrate a convenient syntheticapproach to synthesize R2Mn2O7 pyrochloresat ambient pressure. A series of pyrochlores (R = Y, Ho-Lu)were prepared by a simple and cost-effective molten salt method usingNaCl and KCl as the flux. Moreover, phase-selectivity was demonstratedfor yttrium manganese oxides (YMnO3 and Y2Mn2O7) by a simple variation of synthesis temperatureand precursors-to-chlorides ratio. The synthetic procedure does notrequire high pressures or temperatures nor oxygen flow. All synthesizedpyrochlores demonstrated ferromagnetic behavior at low temperature,and the magnetic properties were in good agreement with those of high-pressure-synthesizedmaterials. The versatility of the method was confirmed by the preparationof a mixed-rare earth Y0.4Er0.4Tm0.4Yb0.4Lu0.4Mn2O7 solidsolution a compositionally complex high-entropy oxide.

Automated summary

Rare-earth manganese pyrochlores (R2Mn2O7), frustrated magnetic materials previously accessed only by high-pressure and high-temperature synthesis, were successfully prepared using a simple molten salt method at ambient pressure. The synthetic procedure did not require high pressures, temperatures, or oxygen flow. The method's versatility was demonstrated by the preparation of a mixed rare-earth solid solution and phase-selectivity for yttrium manganese oxides.