Among these compounds, preferred are a polysilazane in which the Si atom is bound to an alkoxyl group or the like, a polysilazane having an organic group such as an alkyl group, and a perhydropolysilazane in which all of R1, R2, and R3 in the following formula (2) are hydrogen, and more preferred is the perhydropolysilazane, which is easily converted to silica in the below-described formation of t