title: The influence of temperature, pressure and Ag doping on the physical properties of TiO2nanoceramics.
abstract: Undoped and Ag-doped TiO2ceramics have been prepared at temperatures between 500-1000 °C and under pressures up to 8 GPa. Their crystal structures and physical properties were investigated by means of EDX, SEM, TEM, X-ray powder diffraction, and magnetization M, specific heat Cpand electrical resistance ρ measurements. It is found that the anatase-structured As-cast powder transforms into rutile and columbite-type at 500 °C and 5.5 GPa. The stabilization of the latter phase is fulfilled under a pressure of 8 GPa and at temperatures above 800 °C. On the basis of experimental results, we conclude that the physical properties of TiO2can be tailored along with its crystal structure. In particular, magnetic properties change from paramagnetic in anatase and rutile to magnetic correlations and in all likelihood magnetic-field-induced antiferromagnetic short-range order in columbite-structured TiO2. Contrasting behaviour in the temperature dependences of specific heat between anatase/rutile and columbite-type TiO2is obvious. Differently from anatase/rutile, the Cpof columbite-type TiO2exhibits a low-temperature excess, being interpreted as due to magnetic correlations, or else the prevalence of soft modes. An analysis of ρ(T) for columbite-type TiO2in the temperature range of 280-400 K reveals the presence of a new trapping state at an energy level of ∼28 meV within the originally forbidden gap. Furthermore, thermal fluctuation-induced tunnelling and hopping conductivities are suggested to govern in a lower temperature range. We recognize that the Ag-doped contents do not alter the crystal structure but considerably enhance magnetic correlations, compared to undoped samples.
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-422 Wrocław, Poland. V.H.Tran@int.pan.wroc.pl P.Gluchowski@int.pan.wroc.pl A.Lukowiak@int.pan.wroc.pl W.Strek@int.pan.wroc.pl.
authors.forename: V H
authors.initials: VH
authors.lastname: Tran
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-422 Wrocław, Poland. V.H.Tran@int.pan.wroc.pl P.Gluchowski@int.pan.wroc.pl A.Lukowiak@int.pan.wroc.pl W.Strek@int.pan.wroc.pl.
authors.forename: P
authors.initials: P
authors.lastname: Głuchowski
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-422 Wrocław, Poland. V.H.Tran@int.pan.wroc.pl P.Gluchowski@int.pan.wroc.pl A.Lukowiak@int.pan.wroc.pl W.Strek@int.pan.wroc.pl.
authors.forename: A
authors.initials: A
authors.lastname: Łukowiak
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-422 Wrocław, Poland. V.H.Tran@int.pan.wroc.pl P.Gluchowski@int.pan.wroc.pl A.Lukowiak@int.pan.wroc.pl W.Strek@int.pan.wroc.pl.
authors.forename: W
authors.initials: W
authors.lastname: Strȩk