A slurry composition for forming a layer is provided. The slurry composition includes 100 parts by weight of a metal oxide selected from the group consisting of MgO, CaO, SrO, BaO, ZrO.sub.3, and a combination thereof; 1-200 parts by weight of a binding agent per 100 parts by weight of the metal oxide, the binding agent being selected from the group consisting of calcium phosphate (CaP), a calcium-barium-boron-based (CBB-based) oxide, a triple carbonate ((Ca, Ba, Sr)CO.sub.3), and a combination thereof; 1-10 parts by weight of a binder per 100 parts by weight of the metal oxide, the binder being selected from the group consisting of nitro cellulose, ethyl cellulose, methyl methacrylate, and a combination thereof; and 50-500 parts by weight of a solvent per 100 parts by weight of the metal oxide.