Appendix A xA Supporting information Supplementary dataHelp

2. Experimental section
2.1. Synthesis of Ca5Co4V6O24
2.2. Synthesis of Ca5Ni4V6O24
Similar to Ca5Co4V6O24, single crystals of Ca5Ni4V6O24 were obtained using Bruceine A mixture of CaCO3 (3 N, 1.2712 g), Ni(AC)2 (2 N, 2.4856), and V2O5 (3 N, 1.4063 g) as the starting materials. The mixture was ground well and packed into an alumina crucible with a cover. After the furnace was heated up to 950 °C and kept at 950 °C for 12 h, the furnace was slowly cooled to 450 °C at a rate of 5 °C/h and then cooled to room temperature at a rate of 50 °C/h. With this procedure, yellow crystals of Ca5Ni4V6O24 were obtained by mechanical separation from the quartz tube. Powdered samples were synthesized at 600 °C in air with several intermediate grindings using a mixture of CaCO3, NiO, and V2O5 with a molar ratio of 5:4:6. The product was finally sintered at 850 °C for two days. The quality of samples was confirmed by powder X-ray diffraction (Fig. S1).