Unusual Compression Behavior of Nanocrystalline CeO2
نویسندگان
چکیده
The x-ray diffraction study of 12 nm CeO2 was carried out up to ~40 GPa using an angle dispersive synchrotron-radiation in a diamond-anvil cell with different pressure transmitting medium (PTM) (4:1 methanol: ethanol mixture, silicone oil and none) at room temperature. While the cubic fluorite-type structure CeO2 was retained to the highest pressure, there is progressive broadening and intensity reduction of the reflections with increasing pressure. At pressures above 12 GPa, an unusual change in the compression curve was detected in all experiments. Significantly, apparent negative volume compressibility was observed at P = 18-27 GPa with silicone oil as PTM, however it was not detected in other circumstances. The expansion of the unit cell volume of cubic CeO2 was about 1% at pressures of 15-27 GPa. To explain this abnormal phenomenon, a dual structure model (hard amorphous shell and relatively soft crystalline core) has been proposed.
منابع مشابه
Size Dependence of Electrical and Thermal Transport Properties in Oxides
The awareness of environmental factors, limited energy resources, and increasing energy demands have driven the search for both improved utilization of our fossil energy and new alternative energy resources. These new energy technologies are preferably cleaner, cheaper, smaller and more efficient than those currently being employed, for instance fuel cells, lithium-ion batteries, thermoelectric...
متن کاملPressure induced increase of particle size and resulting weakening of elastic stiffness of CeO2 nanocrystals
We demonstrate that the compressibility of cubic fluorite-structure CeO2 nanocrystals s10 nmd increases at pressures above ,20 GPa. At ambient pressure, CeO2 nanocrystals exhibit larger cell parameters than micro-sized samples, and initially exhibit a higher bulk modulus of 328s12d GPa. However, above 20 GPa, the bulk modulus is reduced to 230s10d GPa. Thus, a critical pressure of ,20 GPa was d...
متن کاملAtomic-scale structure of nanocrystalline CeO2–ZrO2 oxides by total x-ray diffraction and pair distribution function analysis
Total x-ray diffraction and atomic pair distribution function analysis have been used to determine the atomic ordering in nanocrystalline (∼1.5 nm in size) CeO2–ZrO2 prepared by a sol–gel route. Experimental data show that the oxides are a structurally and chemically inhomogeneous mixture of nanoscale domains with cubic-type and monoclinic-type atomic ordering, predominantly occupied by Ce and ...
متن کاملEFFECT OF CeO2 DOPING ON THE STRUCTURE, ELECTRICAL CONDUCTIVITY AND ETHANOL GAS SENSING PROPERTIES OF NANOCRYSTALLINE ZnO SENSORS
Nanocrystalline sensors having the general formula ZnO + x wt% CeO2, where x = 0, 2, 4 and 6 were prepared by chemical precipitation method and sintered at 400, 600 and 800 C for 2h in static air atmosphere. The crystal structure and the morphology of the prepared samples were investigated and characterized by using XRD, IR, SEM and TEM techniques. The investigation revealed that the average cr...
متن کاملThe structural origin of the unusual compression behaviors in nanostructured TiO2: insights from first-principles calculations.
First-principles calculations of anatase structured TiO2 and ZrO2 as well as of TiO2-B were carried up to 20 GPa in order to develop an understanding of the unusual compression and pressure-dependent phase transitions reported for nanocrystalline (nc) pure and Zr-doped anatase and nc TiO2-B. The computations, carried out using two global hybrid density functional-Hartree-Fock formulations and a...
متن کامل