Bidimensional sodium ionic conduction of oxyborates Na2M2(BO3)2O (M=Al,Ga) and Na2−2xCaxGa2(BO3)2O (x=0.25,0.50)

Crystalline samples of Na2M2(BO3)2O (M=Al,Ga), Na1.5Ca0.25Ga2(BO3)2O and NaCa0.5Ga2(BO3)2O are prepared by conventional high temperature solid state synthesis technique. Temperature dependent impedance spectroscopy measurements are performed. For Na2Al2(BO3)2O and Na2Ga2(BO3)2O, high and low temperature regimes have to be distinguished. Only one regime is observed for the calcium-substituted samples Na1.5Ca0.25Ga2(BO3)2O and NaCa0.5Ga2(BO3)2O.