Free　barium　(Ba)　is　critical　to　the　formation　of　the　active　layer　on　the　surface　of　dispenser　cathode,　which　is　contributed　to　the　electron　emission　properties　of　the　cathode.　The　Ba　in　the　active　layer　of　the　dispenser　cathode　is　generated　by　the　chemical　reaction　between　aluminate　compounds　and　tungsten　(W)　under　vacuum　and　high　temperature.　Nowadays,　the　effect　of　aluminate　compounds　on　the　generation　of　free　Ba　is　not　clear.　In　this　work,　aluminate　impregnants　called　411,　532　and　612　impregnants　were　prepared　by　coprecipitation　method.　The　structure　of　the　dominate　compounds　in　411,　532　and　612　impregnants　were　determined　with　density　functional　theory　(DFT)　calculation　and　Rietveld　structure　refinement.　It　was　found　that　the　dominate　compounds　of　411,　532　and　612　impregnants　are　Ba3.5Ca0.5Al2O7,　Ba5CaAl4O12　and　Ba3CaAl2O7,　respectively.　Then,　the　temperature　dependence　of　the　thermodynamic　properties,　such　as　Debye　temperature,　entropy,　heat　capacity　and　enthalpy,　of　the　aluminate　compounds　were　calculated.　Based　on　the　thermodynamic　properties,　the　potential　chemical　reaction　between　aluminate　compounds　and　W　are　energetically　determined　by　deviation　Gibbs　energy.　The　effects　of　different　aluminate　compounds　on　the　free　Ba　generation　were　evaluated　with　the　equilibrium　Ba(g)　amounts　that　generated　by　the　chemical　reactions　between　aluminate　compounds　and　W.　It　is　shown　that　the　equilibrium　Ba(g)　amounts　generated　by　Ba3.5Ca0.5Al2O7　is　higher　than　that　by　Ba5CaAl4O12　and　Ba3CaAl2O7,　implying　the　superiority　of　electron　emission　performance　of　Ba3.5Ca0.5Al2O7.　The　electron　emission　densities　of　the　dispenser　cathodes　that　impregnated　with　the　411,　612　and　532　impregnants　are　5.06,　4.31　and　4.05　A/cm2,　respectively.　It　is　revealed　that　the　Ba3.5Ca0.5Al2O7　has　superiority　in　generating　free　Ba,　which　agreed　well　with　thermodynamic　simulation　results.　©　2024