“…According to the solid-state method, the lead sodium apatite Pb 8 Na 2 (PO 4 ) 6 was synthesized at 500 °C for three days, then the temperature was increased to 1000 °C for 12 hours, and finally it was decreased to 500 °C. 28 In other works, [29][30][31] lead sodium apatite compounds Pb (8-x) Ln x Na 2 (PO 4 ) 6 O (x/2) and Pb (8-x) Ln x Na 2 (GO 4 ) 6 (2-x/2) O (x/2) were obtained by solidstate method with a large variety of rare earth element substitutions (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, Y) for lead (Pb). The calcined time ranged from 7 hours at 900 °C to 50-250 hours at 800 °C.…”