Abstract Positive temperature coefficient resisitivity effect is formed by grain boundary in polycrystaline semiconducfive ceramics, while grain boundary barrier depends on the energy levels of the acceptor surface state and the defect distribation formed by barium vacancy in the samples.
The (NH4)2Sx wet passivation treatment effectively removes the oxide and excess As from the surface and thereby suppresses the donor type antisite defects AsGa formation. In other words, the (NH4)2Sx treatment reduces the Nd and the ratio of Nd/Na, where Na is the concentration of acceptor-type defects, and Nd is the concentration of donor-type defects. The increase of acceptor states in the surface increases the density of the negative charge.
Acccording to Heywang model,the acceptor-state density N(so),and the height of the grain- boundary potential barriers at different temperatures were quantitatively calculated.
On the basis of the test,the nature of surface state of BaTiO_3 ceramic is discussed and it is pointed that the surface state of the acceptor is (V_(Ba))~" and absorbed O~(2-).