Thermal and environmental barrier coating for ceramic substrates

An article, comprising:

• a ceramic substrate;
• a thermal barrier coating covering a surface of the ceramic substrate, the thermal barrier coating having:
• a void volume fraction of at least 60% and a major part of the void volume being closed porosity,
• the thermal barrier coating comprising, as a major component, a plurality of hollow particles, the plurality of hollow particles comprising, as a major component, a rare-earth silicate,
• each of the plurality of hollow particles having:
• a maximum interior dimension less than 1 millimeter (mm) and greater than 5 micrometers, and
• a maximum wall thickness less than 1/10 of the maximum interior dimension,
• wherein the plurality of hollow particles are embedded in a matrix and the material of the matrix is selected from the group consisting of:
• rare-earth gallates, hafnium titanates, zirconium titanates, scandium tantalates, and combinations thereof;
• and
• a capping layer covering a portion of a surface of the thermal barrier coating, the capping layer having a porosity less than 10% and a thickness less than 1/10 of the thickness of the thermal barrier coating, and wherein the capping layer comprises the same rare-earth silicate as the plurality of hollow particles, and wherein the same rare-earth silicate is selected from the group consisting of yttrium monosilicate (Y2SiO5), yttrium disilicate (Y2Si2O7), ytterbium monosilicate (Yb2SiO5), ytterbium disilicate (Yb2Si2O7), and scandium disilicate (Sc2Si2O7).