Sodium additions have been shown to increase the conductivity for both Ca3Co4O954, 80 and Ca3Co2O6.67 The increase in Seebeck coefficient of Ca3O4O9 with sodium additions alone is small 54,80 but can be increased by co-doping with manganese. 81 Co-doping of sodium with neodymium can also lead to an increase in thermopower, as well as a decrease in thermal conductivity, but in this case the electrical conductivity is decreased. 71 Like sodium, potassium additions to Ca3O4O9 lead to an increase in electrical conductivity with only a slight increase in Seebeck coefficient and an increase in thermal conductivity, the net result of which is a modest increase in the figure of merit. 44,75 Co-doping of potassium with lanthanum has been shown to increase the electrical conductivity without significantly affecting the Seebeck coefficient. 75