Temperature induced delocalization of charge carriers and metallic phase in Co0.6Sn0.4Fe2O4 nanoparticles J. Appl. Phys. 112, 063718 (2012) Negligible carrier freeze-out facilitated by impurity band conduction in highly p-type GaN Appl. Phys. Lett. 101, 082106 (2012) Anderson localization in strongly coupled gold-nanoparticle assemblies near the metal-insulator transition Appl. Phys. Lett. 101, 083105 (2012) Epitaxial growth and metal-insulator transition of vanadium oxide thin films with controllable phases Appl. Phys. Lett. 101, 071902 (2012) Relationship between variable range hopping transport and carrier density of amorphous In2O3-10wt. % ZnO thin filmsWe report that the first-order metal-insulator (MI) transition in perovskite ruthenate Ca 2 RuO 4 can be tuned to a nearly second order transition with the transition temperature close to room temperature via Sr, Ti, and Fe chemical doping. The resistivity near this transition ranges from 10 À2 À 10 À1 X-cm. The maximum temperature coefficient of resistance TCR(¼ À(1/R)dR/dT near the transition exceeds 0.4 K À1 . This MI transition can also be tuned by a relatively small biascurrent. These properties suggest that doped calcium ruthenates can be considered an alternative material for improving upon existing bolometric technologies. V C 2012 American Institute of Physics. [http://dx.