A material having a negative or low thermal expansion coefficient and composed substantially of a single crystal system is provided.The material is an oxide represented by the chemical formula ((R.sup.4+M.sup.2+).sub.1-xA.sup.3+.sub.2x)(QO.sub.4).sub.3 (where R stands for at least one tetravalent metal element selected from Zr and Hf; M stands for at least one divalent metal element selected from Mg, Ca, Sr, Ba, and Ra; Q stands for at least one hexavalent metal element selected from W and Mo; and A stands for at least one trivalent metal element selected from Al, Sc, Y, Lu, Ga, and In; 0