In this paper, Nb-doped BaTiO3-(Na0.5Bi0.5)TiO3(BBNT-Nb) based PTCR ceramic material has been prepared using high purity Nb2O5, Bi2O3, Na2CO3,TiO2and BaTiO3powders as starting materials, and its structural and electrical properties are investigated. The results indicated that the Nb2O5dopant is helpful not only to promote the formation of tetragonal BBNT structure without any second phase, but also to decrease the room-temperature resistivity. For the 0.10at% Nb-doped BBNT material with BNT content 35mol%, the properties of room-temperature resistance of 104Ω·cm, temperature coefficient (αk) of 6.3%/°C, PTCR anomaly lg(Rmax/Rmin) of 3.6 and Curie temperature (Tc) of 193°C are obtained.

In this paper, Na+-doped silicon clathrate thin films were prepared on Si substrate by sol-gel method using zinc acetate and sodium carbonate as starting materials and the effects of the growth conditions on the structural of the films have been investigated by XRD, HRTEM, SAED analysis. The XRD results showed that there only existed a narrow and sharp peak around 2θ=32.94º which was assigned as the diffraction of Na8Si46(321). However, the peak at 2θ=32.94º disappeared when it was heated to above 640°C due to the decomposition of the silicon clathrates. Minute Zn2+ions in the gel was proved to promote the formation of Na-doped silicon clathrates. The HRTEM photos revealed that the thickness of the films was only about 15nm, and there existed no obvious interfaces between the film and the silicon substrate.

Perovskite-structured (Bi1/2Na1/2)TiO3 (BNT) ferroelectric with Curie temperature about 320°C is considered to be a good candidate of high temperature lead-free materials with a positive temperature coefficient of resistance (PTCR). In this study, lead-free PTCR ceramics with compositions of (1-x)BaTiO3-x(Bi1/2Na1/2)TiO3 (BT-BNT x=0.5-55mol%) were successfully prepared without any additional donor or acceptor dopants. The effects of BNT content on the Curie temperature Tc and the PTC effect of the ceramic materials were investigated. The X-ray diffraction data indicated that BT phase and BNT phase formed a solid solution during sintering even though the x value was up to 55mol%. The Curie temperature Tc of the samples increased from ~130°C to ~216°C with the increase of the BNT amount (x value) from 0.5mol% to 40mol%. However, it decreased when excess BNT was added (x value increased from 40mol% up to 55mol%), which was resulted from the volatile effects of Bi3+ and Na+ ions during sintering. The sample of 0.6BaTiO3- 0.4(Bi1/2Na1/2)TiO3 with Tc =216°C, room-temperature resistivity 104 Ω·cm and Rmax/Rmin= 102.7 was obtained. There is a relationship between the Curie temperature and the cell volume of the perovskite structured lattice.