Process for preparing an epitaxial α-quartz layer on a solid support, comprising the following steps: i) a step of preparing a composition containing, in a solvent, at least one silica and/or colloidal silica precursor; ii) a step of depositing a layer of the composition obtained above in step i) onto at least part of the surface of a substrate and the formation of an amorphous silica matrix layer; iii) a step of heat treatment of the amorphous silica matrix layer obtained in step ii) to obtain an epitaxial α-quartz layer, said process being characterized in that: - the substrate is a self-supporting substrate chosen from mono-oriented crystalline silicon, germanium dioxide, corundum, magnesium oxide, strontium titanate, lithium niobiate, lithium tantalate, cerium oxide, gadolinium cerium mixed oxides Ce (1-x) Gd x O 2 in which x is such that 0 < x < 1, lanthanum aluminate, gallium nitride, yttrium-doped zirconium dioxide and gallium orthophosphate, and in that - the step of heat treatment of the amorphous silica layer is performed at a temperature of greater than or equal to 800°C, in the presence of at least one catalyst based on one of the following elements in oxidation state (+2): strontium, barium, calcium, magnesium, beryllium, or one of the following elements in oxidation state (+1): caesium, rubidium, lithium, sodium or potassium, or capable of generating one of the following elements in oxidation state (+2): strontium, barium, calcium, magnesium, beryllium, or one of the following elements in oxidation state (+1): caesium, rubidium, sodium, potassium or lithium, said catalyst being present in said amorphous silica matrix. i) a step of preparing a composition containing, in a solvent, at least one silica and/or colloidal silica precursor; ii) a step of depositing a layer of the composition obtained above in step i) onto at least part of the surface of a substrate and the formation of an amorphous silica matrix layer; iii) a step of heat treatment of the amorphous silica matrix layer obtained in step ii) to obtain an epitaxial α-quartz layer, said process being characterized in that: - the substrate is a self-supporting substrate chosen from mono-oriented crystalline silicon, germanium dioxide, corundum, magnesium oxide, strontium titanate, lithium niobiate, lithium tantalate, cerium oxide, gadolinium cerium mixed oxides Ce (1-x) Gd x O 2 in which x is such that 0 < x < 1, lanthanum aluminate, gallium nitride, yttrium-doped zirconium dioxide and gallium orthophosphate, and in that - the step of heat treatment of the amorphous silica layer is performed at a temperature of greater than or equal to 800°C, in the presence of at least one catalyst based on one of the following elements in oxidation state (+2): strontium, barium, calcium, magnesium, beryllium, or one of the following elements in oxidation state (+1): caesium, rubidium, lithium, sodium or potassium, or capable of generating one of the following elements in oxidation state (+2): strontium, barium, calcium, magnesium, beryllium, or one of the following elements in oxidation state (+1): caesium, rubidium, sodium, potassium or lithium, said catalyst being present in said amorphous silica matrix. - the substrate is a self-supporting substrate chosen from mono-oriented crystalline silicon, germanium dioxide, corundum, magnesium oxide, strontium titanate, lithium niobiate, lithium tantalate, cerium oxide, gadolinium cerium mixed oxides Ce (1-x) Gd x O 2 in which x is such that 0 < x < 1, lanthanum aluminate, gallium nitride, yttrium-doped zirconium dioxide and gallium orthophosphate, and in that - the step of heat treatment of the amorphous silica layer is performed at a temperature of greater than or equal to 800°C, in the presence of at least one catalyst based on one of the following elements in oxidation state (+2): strontium, barium, calcium, magnesium, beryllium, or one of the following elements in oxidation state (+1): caesium, rubidium, lithium, sodium or potassium, or capable of generating one of the following elements in oxidation state (+2): strontium, barium, calcium, magnesium, beryllium, or one of the following elements in oxidation state (+1): caesium, rubidium, sodium, potassium or lithium, said catalyst being present in said amorphous silica matrix.