Is silicon dioxide decomposition possible?
Silicon dioxide is difficult to decompose directly, but it can be broken down in the presence of other reagents at more moderate temperatures.  In particular, the reaction of silica with elemental silicon has been known since 1905:

In 1890, the German chemist Clemens Winkler (the discoverer of germanium) was the first to attempt to synthesize $\ce{SiO}$ by heating silicon dioxide with silicon in a combustion furnace.[1]
$$\ce{SiO2 + Si ⇌ 2 SiO}$$
However, Winkler was not able to produce the monoxide since the temperature of the mixture was only around 1000° C. The experiment was repeated in 1905 by Henry Noel Potter (1869–1942), a Westinghouse engineer. Using an electric furnace, Potter was able to attain a temperature of 1700° C and observe the generation of $\ce{SiO}$.[2] Potter also investigated the properties and applications of the solid form of $\ce{SiO}$.[3,4]

The reaction may be used to remove silica from ores.
Cited references:

C. Winkler Ber. 23, (1890) p. 2652.

J. W. Mellor &quot;A Comprehensive Treatise on Inorganic and Theoretical Chemistry&quot; Vol VI, Longmans, Green and Co. (1947) p. 235.

U.S. Patent 182,082, July 26, 1905.

E. F. Roeber H. C. Parmelee (Eds.) Electrochemical and Metallurgical Industry, Vol. 5 (1907) p. 442.  Link