Provided are a dielectric, a device including the same, and a method of preparing the dielectric. The dielectric material includes a NaNbO3 ternary material including a perovskite phase with a Sm element substituted into a Na site such that the NaNbO3 ternary material has a permittivity of 600 or more at 1 kHz, and a temperature coefficient of capacitance (TCC) of about -15% to about 15% in a range of about -55° C. to about +200° C.