In Situ Time‐Resolved Neutron Diffraction Investigation during Oxygen Exchange in Layered Cobaltite Cathode Materials

Abstract

The development of in situ techniques for the characterization of solid phases is becoming one of the major issues in current research on materials. This interest relates to the increasing requirement of getting a deeper insight into the changes that occur when a chemical or physical transformation or reaction takes place in the sample under investigation. Time-resolved structural characterization is a valuable tool in this respect, and usually such techniques are used to study the reaction kinetics at a defined reaction temperature, [1][2][3] mainly by means of X-ray diffraction (XRD). On the other hand, neutron diffraction (ND) is a valuable tool to investigate oxides owing to the sensitivity of neutrons to light atoms such as oxygen and to the possibility of revealing superstructure peaks. Highly studied materials which benefit from the investigation through ND are solid-state ionic (SSI) materials (mainly electrolytes and mixed ionic-electronic materials) for which, for example, the study of oxygen-exchange processes are of great importance to test their performance and define the temperature range for their potential application. To date, to the best of our knowledge, there are no available experimental probes to study the structural evolution of a crystalline solid during oxygen-exchange processes. As the investigated material undergoes a structural change during the diffusion of oxygen into or out of it, it would be highly desirable to develop a method able to simultaneously study the oxygen content variation profile and the structural variation occurring in the sample. This technique could pave the way for extraction of new and essential information on the phenomena occurring during oxygen exchange and can be of relevance for the comprehension of the oxygen migration mechanism and, therefore, could guide the design of optimized compositions.In view of these relevant applications, we have devised and carried out time-resolved in situ neutron diffraction (ND) measurements under isothermal conditions and with varied oxygen partial pressure p(O 2 ) inside the measurement apparatus. By recording neutron patterns at proper time intervals it is possible, through the refinement of oxygen occupancies, to determine the concentration profile during oxygen exchange and, at the same time, to have a clear insight into the structural changes occurring in the sample when oxygen is introduced or removed. To our knowledge, our experiment is the first of this kind carried out on any material. Herein we present the result of the experimental work, thus showing the feasibility of this approach to the study of SSI materials and, in general, of any nonstoichiometric oxygencontaining compound. It is clear that this method can also be applied to the in situ time-resolved study of any species that can be easily probed by neutrons, such as hydrogen and deuterium, thus opening new possibilities, for example in the field of hydrogen storage materials.The compound investigated herein is the HoBaCo 2 O 5+d layered cobaltite. Recently t...

Layered LaSrGa3O7‐Based Oxide‐Ion Conductors: Cooperative Transport Mechanisms and Flexible Structures

“…Research in the area of oxide-ion conductors has concentrated primarily on fluorite-type oxides (such as Y-doped ZrO 2 or Gd-doped CeO 2 ), and perovskite-type oxides (such as doped LaGaO 3 ), in which oxygen transport proceeds through conventional hopping between oxygen vacancy defects. [1][2][3][4][5][6] However, there is growing interest in developing alternative electrolytes with lower operating temperatures (600-700°C). [6,7] In particular, novel compounds showing high oxide-ion conductivity, such as apatite-structured La 9.33+x Si 6 O 26+3x/2 , [8][9][10][11] as well as structures containing tetrahedral moieties that include the gallate La 1-x Ba 1+x GaO 4-x/2 , [12] have been attracting considerable attention.…”