Silica-rich barrier coatings

A method comprising:

• depositing, via air plasma spraying, a plurality of particles directly on a silicon bond layer that is on a ceramic or ceramic matrix composite (CMC) substrate to form a silica-rich barrier coating directly on the silicon bond layer on the ceramic or CMC substrate, the plurality of particles including a silica-rich rare earth (RE) disilicate material and a second material, wherein the second material comprises LiREO2, wherein the silicon bond layer is directly on the ceramic or CMC substrate and the silica-rich barrier coating is directly on the silicon bond layer,
• wherein the silica-rich RE disilicate material includes excess silica compared to a stoichiometric RE disilicate material,
• wherein the silica-rich barrier coating includes a first domain having a granular structure, respective grains of the granular structure including the silica-rich RE disilicate material,
• wherein the silica-rich barrier coating includes a second phase, the second phase including the LiREO2 and being disposed at grain boundaries defined by the granular structure of the first domain of the barrier coating, wherein the second phase includes a glassy phase formed by reaction of the LiReO2 with at least a portion of the excess silica, wherein the LiREO2 and the glassy phase in the silica-rich barrier coating are present in an amount to increase the hermeticity of the silica-rich barrier coating and provide oxidation protection to the silicon bond layer and/or the substrate underlying the silica-rich barrier coating,
• wherein the silica-rich barrier coating comprises predominantly the first domain and less than about 30 vol. % of the second phase;
• and
• forming an environmental barrier coating layer directly on a top surface of the silica-rich barrier coating such that a layer interface is formed between the environmental barrier coating layer and the top surface of the silica-rich barrier coating, wherein the environmental barrier coating layer includes a silicate-lean RE silicate without excess silica compared to the stoichiometric RE silicate material, wherein the environmental barrier coating layer includes RE monosilicate.