A Nicolet-200SXV FT-IR spectrometer combined with an exciting light set-up has been applied to determine the shallowimpurity concentration in detector--grade si
YBa<sub>2</sub>Cu<sub>3</sub> O<sub>7-x</sub>(YBCO) is one of thesuperconducting oxides with transition tem-perature above 90K.It has a orthorhombic crystal struc