Investigation of the perovskite ceramic Li0.30La0.56TiO3 by Pulsed Force Mode AFM for pH sensor application

Depending on the sintering temperature, Li0.30La0.56TiO3 ceramics are either sensitive or insensitive to the pH of aqueous solutions. These ceramics may then be used as pH sensor and reference electrode in an all solid state combined pH electrode device. To shed some light on the mechanism of the ceramics pH sensitivity or insensibility, we have studied the surface properties of both types of ceramics, at a local scale. We have performed adhesion and topographic surface images by means of an atomic force microscope (AFM) in the Pulsed Force Mode (PFM). The interpretation of the AFM images is discussed in terms of both surface roughness and capillary force. In particular, adhesive surface property images show that the sensitive ceramics exhibit higher hydrophilic surface properties than the insensitive ones. Such hydrophilic character can be attributed to the basic hydroxyl –OH groups present at the surface of the sensitive ceramics. Finally, some attempts are given to understand the mechanism of the pH behaviour of these oxides.