Decrement of Piezoelectric Constants Caused by Screening Effect of Conduction Electrons on the Effective Charge of CdS Crystals

Decrement of piezoelectric constants in n -CdS crystals is observed as a function of conductivity. The decrement of the constants is closely related to the increment of the electrical conductivity with a one-valued function in a range between 10 -8 and 10 ohm -1 cm -1 . For example, the piezoelectric constant in a CdS crystal with 10 ohm -1 cm -1 is only 40% of that with 10 -8 ohm -1 cm -1 . This phenomenon is theoretically explained by the decrement of the effective charge on Cd or S ions caused by the Thomas-Fermi screening of conduction electrons in n -CdS crystals.