Environmental　barrier　coatings　(EBCs)　can　effectively　protect　SiC-based　ceramic　matrix　composites　(CMC-SiC)　from　high-temperature　water　vapor　corrosion　in　aero-engines.　Rare-earth　pyrosilicates　(RE2Si2O7)　have　become　one　of　the　most　promising　EBC　materials　owing　to　their　coefficient　of　thermal　expansion　(CTE),　which　is　similar　to　that　of　CMCs,　and　their　excellent　high-temperature　performance.　However,　RE2Si2O7　is　prone　to　cracking　during　thermal　cycling,　and　its　ability　to　resist　high-temperature　water　vapor　corrosion　is　insufficient.　High-entropy　silicate　materials　prepared　by　mixing　multiple　rare-earth　elements　tend　to　exhibit　better　thermo-physical　properties　and　high-temperature　water　vapor　corrosion　resistance.　A　new　type　of　high-entropy　ceramics　(Yb0.25Lu0.25Tm0.25Y0.25)2Si2O7　((4RE0.25)2Si2O7)　is　synthesized　using　four　rare-earth　elements　for　a　high-entropy　design.　In　terms　of　element　selection,　pyrosilicates　with　the　rare-earth　elements　Yb　or　Lu　have　stable　single　β　crystal　polymorphs　and　excellent　resistance　to　high-temperature　water　vapor　corrosion.　In　addition,　pyrosilicates　with　rare-earth　elements　Tm　or　Y　have　β　crystal　polymorph　at　high　temperatures,　and　β-Y2Si2O7　has　lower　thermal　conductivity.　Therefore,　(4RE0.25)2Si2O7　is　likely　to　crystallize　in　a　single　β　crystal　polymorph.　The　microstructure,　phase　composition,　thermal　properties,　and　resistance　to　water　vapor　corrosion　are　systematically　investigated.　The　experimental　results　show　that　(4RE0.25)2Si2O7　bulks　with　monoclinic　β-phase　are　successfully　prepared　by　non-pressure　sintering.　The　doped　rare-earth　elements　are　uniformly　distributed　in　the　matrix,　and　no　obvious　component　segregation　occurs.　In　addition,　the　atomic　proportion　of　each　element　in　(4RE0.25)2Si2O7　is　close　to　the　theoretical　value.　The　thermal　gravimetric　(TG)　curve　remains　horizontal　without　obvious　weight　changes　from　room　temperature　to　1300　°C.　There　are　no　obvious　absorption/exothermic　peaks　in　the　differential　scanning　calorimetry　(DSC)　curve,　indicating　that　no　phase　transition　or　decomposition　occurs　during　heating.　It　has　a　low　CTE　(2.66×10−6–3.84×10−6　℃−1).　The　CTE　of　(4RE0.25)2Si2O7　increases　with　increasing　temperature　but　is　lower　than　that　of　Yb2Si2O7　at　all　temperatures.　It　can　also　be　applied　to　substrates　with　a　lower　CTE,　such　as　Si3N4　(3×10−6–4×10−6　°C−1).　The　thermal　diffusion　coefficient　(0.41–0.92　mm2/s)　is　lower　than　that　of　Yb2Si2O7.　Below　500　°C,　the　thermal　conductivity　decreases　as　the　temperature　increases.　When　the　temperature　is　higher　than　500　°C,　the　thermal　conductivity　increases　rapidly　with　the　increase　in　temperature　because　of　the　increased　effect　of　thermal　radiation,　which　causes　the　thermal　conductivity　of　(4RE0.25)2Si2O7　to　exceed　that　of　Yb2Si2O7　above　800　°C.　To　compare　the　performance　of　the　synthesized　(4RE0.25)2Si2O7　in　a　high-temperature　water　vapor　environment,　Yb2Si2O7,　which　has　been　proven　to　exhibit　good　water　vapor　corrosion　resistance,　is　selected　as　the　control　group.　In　the　atmosphere　of　90%Air-10%H2O　at　1300　°C　for　200　h,　the　weight　loss　of　(4RE0.25)2Si2O7　is　significantly　lower　than　that　of　Yb2Si2O7,　with　negligible　weight　loss　from　180　to　200　h.　The　weight　loss　is　only　0.625　mg/cm2,　which　indicates　that　the　(4RE0.25)2Si2O7　bulk　is　not　liable　to　react　with　water　vapor.　After　200　h　of　water-vapor　corrosion,　(4RE0.25)2Si2O7　remains　single　and　stable　without　any　phase　transition.　It　contains　a　small　amount　of　Y2SiO5　impurities　before　corrosion,　which　disappear　after　water　vapor　corrosion.　The　slight　reaction　between　Y2SiO5　and　H2O,　which　generates　gaseous　Y(OH)3　and　Si(OH)4,　is　the　main　reason　for　the　weight　loss　in　the　high-entropy　ceramic　bulk.　There　is　no　significant　difference　between　the　EDS　energy　spectra　before　and　after　corrosion.　After　corrosion,　it　can　be　observed　that　Yb,　Lu,　and　Tm　are　evenly　distributed,　whereas　Y,　Si,　and　O　are　concentrated　in　the　areas　without　pores,　which　demonstrates　that　the　formation　of　pores　is　related　to　Y2SiO5.　Doping　multiple　rare-earth　elements　into　the　lattice　of　Yb2Si2O7　reduces　the　diffusion　rate　of　atoms,　resulting　in　better　phase　stability　in　high-entropy　ceramics.　These　excellent　properties　demonstrate　that　high-entropy　silicate　ceramics　prepared　according　to　the　properties　of　different　rare-earth　elements　have　promising　potential　in　terms　of　their　thermal　properties,　which　lays　the　foundation　for　their　practical　application.　©　2024　Chinese　Mechanical　Engineering　Society.　All　rights　reserved.