Environmental barrier coating and related articles and methods

An article comprising:

• a substrate comprising silicon;
• a bondcoat, comprising elemental silicon or a silicide, disposed over the substrate;
• an intermediate coating system disposed over the bondcoat, comprising
• a barrier layer comprising an aluminosilicate, wherein at least about 50% by volume of the aluminosilicate is hexacelsian barium strontium aluminosilicate, amorphous barium strontium aluminosilicate, or mixtures of the two;
• a top separator layer comprising elemental silicon or a silicide disposed over the intermediate coating system;
• and
• a topcoat, comprising at least about 80% by volume monoclinic celsian barium strontium aluminosilicate, disposed over the top separator layer.

A method for fabricating an article, comprising:

• providing a substrate;
• disposing an intermediate coating system over the substrate, the system comprising
• a separator layer comprising an oxygen getter material, and
• a barrier layer disposed over the separator layer, the barrier layer comprising a ceramic composition;
• and
• disposing a topcoat over the intermediate coating system, the topcoat comprising the ceramic composition;
• wherein at least about 50% by volume of the ceramic composition present in the barrier layer is a metastable precursor material having the tendency to transform over time into a product material, wherein at least about 75% by volume of the ceramic composition present in the topcoat is the product material, and wherein up to about 25% by volume of the ceramic composition present in the topcoat is the metastable precursor material.