CBSE Class 12-science Answered
(i) Paramagnetism: Materials which are weakly attracted by magnetic fields are called paramagnetic materials and the property thus exhibited is called paramagnetism. Paramagnetic substances contain unpaired electrons, e.g. TiO, CuO, O2 and VO2 etc.
(ii) Piezoelectric effect: When electricity is produced due to the displacement of ions, on the application of mechanical stress, or the production of mechanical stress and/or strain due to atomic displacement on some polar crystals on the application of electric field, it is known as piezoelectric effect. Quartz shows this property.
(iii) Frenkel defect in crystals: Frenkel defect occurs when an atom or ion (generally cation) leaves the normal site in the crystal lattice (creating a vacancy) and occupies on interstitial site. This defect is generally found is silver halides like AgCl, AgBr etc because of the small size of Ag+ ions.