Rare-earth　zirconates　(RE2Zr2O7)　are　potential　thermal　barrier　coatings　(TBCs)　candidates　exhibiting　excellent　thermal　insulation　property　to　protect　underlying　superalloy　substrate.　These　coating　materials,　however,　are　subjected　to　degradation　caused　by　molten　silicon-containing　sand　dust　and　volcanic　ash　whose　main　compositions　are　CaO-MgO-AlO1.5-SiO2　(brief　to　CMAS)　at　higher　operating　temperatures　(＞　1200ºC).　Here,　we　have　studied　the　thermochemical　interactions　between　three　RE2Zr2O7　(Sm2Zr2O7,　Gd2Zr2O7　and　Yb2Zr2O7)　and　CMAS　with　three　different　compositions　(referred　to　as　CMAS-1,　CMAS-2　and　CMAS-3,　respectively)　at　1300ºC/30　min.　Both　the　diversities　of　the　REO1.5　identity　and　CMAS　composition　result　in　the　precipitation　of　apatite　with　varying　stoichiometry.　For　an　equivalent　CMAS　case,　there　is　a　linear　correlation　between　the　apatite　content　and　the　RE　cation　radius.　In　CMAS-1,　the　Ca:RE　ratio　of　apatite　observed　in　the　Sm2Zr2O7　case　is　∼0.31,　larger　than　that　of　Gd2Zr2O7　(∼0.30)　and　Yb2Zr2O7　(∼0.20).　Additionally,　the　RE3+　solubility　in　equilibrium　with　apatite　decreases　with　the　increased　CaO　content　from　CMAS-3　to　CMAS-1　for　a　given　RE2Zr2O7　material,　facilitating　the　apatite　precipitation　within　a　short　time.　For　example,　in　Sm2Zr2O7　case　the　Sm3+　solubility　decrease　from　∼3.18　at　%　to　∼0.70　at　%　as　the　CaO　content　increases　from　19　mol　%　(　in　CMAS-3)　to　33　mol　%　(　in　CMAS-1).　Also,　the　composition　of　residual　CMAS　melt　changes　as　the　interaction　proceed,　which　can　impact　its　flow　property　and　infiltration　propensity.　These　finds　may　advance　the　design　of　current　and　next-generation　TBCs　material　and　development　of　effective　strategies　to　mitigate　the　CMAS-induced　coating　failure.　©　2023