Ionic conductivities of ion-exchanged alkali metal phosphatoantimonate (A2Sb3P2O14, A = sodium, potassium, rubidium), A5Sb5P2O20 (A =lithium, sodium, potassium, rubidium), and partially substituted potassium phosphatoantimonato niobate or potassium phosphatoantimonato tantalate (K5Sb5-xMxP2O20, M = niobium, tantalum)