Articles having reduced expansion and hermetic environmental barrier coatings and methods for their

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Articles suitable for use as high-temperature machine components include a substrate and an environmental barrier coating disposed over the substrate, where the environmental barrier coating includes at least one hermetic self-sealing layer formed from a mixture including an alkaline earth metal aluminosilicate and a rare-earth silicate, and where the at least one hermetic self-sealing layer exhibits substantially no net remnant or residual expansion when subjected to high temperature heat treatment. The environmental barrier coating can further include a bondcoat disposed between the substrate and the hermetic self-sealing layer, a topcoat disposed over the hermetic self-sealing layer, and/or an intermediate layer disposed between the hermetic self-sealing layer and the bondcoat. The intermediate layer can include a barrier material that is substantially inert with respect to silica.