Investigation of the PTCR effect in ZnO–NiO two-phase ceramics

Thermoelectric properties of ZnO ceramics densified through spark plasma sintering

“…Gautam et al [23] observed similar electrical behaviour on pure ZnO, however, the causes of such behaviour was not reported. Similar behaviour was observed for Ni doped ZnO ceramics at temperatures between 250 450°C, the behaviour was due to thermally induced disconnection of low ohmic chains of ZnO grains by highly resistive NiO phase [50]. In this report the ceramic is pure ZnO, therefore the only plausible explanation is that the metallic behaviour could have been caused by the presence of ZnO defects formed during sintering and/or grain boundary resistance [51].…”

Nanometer‐Scale Variations in Interface Potential by Scanning Probe Microscopy

“…The sample was prepared by using a standard solid-state route, starting from prereacted ZnO SS and NiO SS calcinates with compositions of (Zn 0.97 Ni 0.03 )O and (Ni 0.6 Zn 0.4 )O, respectively. 20 A powder mixture of ZnO SS and NiO SS with a 2:3 weight ratio was then sintered under a pressure of 15 MPa at 1430°C for 2 h. Varistor samples were sectioned from a commercial device that was made of ZnO with usual dopants (bismuth, titanium, cobalt, manganese, etc. ), and the grain size was on the order of 70 m. Both sample types were polished and then micropatterned with an array of metal pads that were designed to isolate individual grain boundaries between each electric contact.…”

New composites of ZnO–P2O5/Ni having PTC transition and high Seebeck coefficient

“…The change of Seebeck coefficient from p to n depends to the composition x and temperature. The same solution have been studied by Lisjak et al [27] and a PTC phase transition has been shown around 673 K above 20 wt.% of ZnO. Then, the PTC phenomenon decreases for high values of x and disappears around 80 wt%.…”