2 Materials and Methods The resulting dry powder mix was subsequently transferred into a platinum crucible, compacted using a pestle, and sealed with a platinum lid. The solid-state reaction was performed in an electrical chamber furnace and comprised 4 synthesis steps: 1. heating to 1000 °C in 6 h (167 °C/h), 2. maintaining the temperature at 1000 °C for 4 h, 3. further heating to 1400 °C over 4 h (100 °C/h), 4. maintaining the temperature at 1400 °C for 6 h. Upon completion of the program, the sample was removed from the oven and rapidly quenched using compressed air. After crushing the synthesis product, an intermediate milling step was conducted, and again, the ground powder was compacted into the crucible. In the second sinter process, the sample was heated to 1400 °C in 8 h (175 °C/h) and then the temperature maintained at 1400 °C over 6 h, followed by quenching, crushing and milling.