Enhanced High-Temperature Electronic Transport Properties in Nanostructured Epitaxial Thin Films of the La_n+1Ni_nO_3n+1 Ruddlesden−Popper Series (n = 1, 2, 3, ∞)

Abstract

Epitaxial thin films of lanthanum nickel oxide Ruddlesden−Popper series (La n +1Ni n O3 n +1) have been prepared on different single-crystal substrates by metal organic chemical vapor deposition. Varying the La/Ni composition ratio in the precursor solution allows deposition of films with controlled La/Ni stoichiometry ranging between 1 and 2. Epitaxial La2NiO4 (n = 1) and LaNiO3 (n = ∞) pure phases were obtained for La/Ni close to 2 and 1, respectively. For intermediate La/Ni composition, films with a microstructure consisting of a disordered stacking of nanodomains with progressively increasing average n value were obtained. Similarly with bulk samples, the electronic conductivity of the nanostructured films increases with the measured average n value, opening the possibility to prepare new mixed ionic and electronic conducting nanocomposite thin films with tailored properties

Thermoelectric properties of electron doped SrO(SrTiO3)n (n=1,2) ceramics

“…The similarities have been reported as well in some other RP systems. 16,17 Above 750 K, the -values drop proportionally to T −1.5 in 100x-Nb-RP n phases ͑x = 0.05-0.2, n =1,2͒ such as in SrTi 0.8 Nb 0.2 O 3 , 2,3 which additionally support the above conclusion on the role of SrTiO 3 layers as the main conduction passage. Apparently, one can see from Fig.…”

Activity and Stability of Ruddlesden–Popper‐Type Lan+1NinO3n+1 (n=1, 2, 3, and ∞) Electrocatalysts for Oxygen Reduction and Evolution Reactions in Alkaline Media

“…Accordingly, the charge‐transfer resistances of these compounds were assessed by electrochemical impedance spectroscopy (EIS) measurements at a potential of 1.65 V versus RHE (i.e., during OER), the responses of which are plotted in Figure c. The similarity between the trends shown by the OER activities and the charge‐transfer resistances suggests that the latter is an important factor for determining OER performance. This is to be anticipated as the room‐temperature electronic conductivity for La n +1 Ni n O 3 n +1 increases with increasing n values as reported elsewhere,– resulting in faster electron transfer for compounds with larger n values. We attribute this to the increased concentration of Ni−O−Ni bonds through which the electronic conduction takes place given the progressive delocalization of the p‐type electronic charge carriers …”

“…Earlier studies discovered that the catalytic activity of these oxides at elevated temperatures (500–900 °C) can be modified and is dependent on the n value –. The presence of oxygen interstitials in the rock‐salt layers promotes fast ionic transport and therefore enhances the ORR activity of this material as the cathode in solid oxide fuel cells –. It is of interest for us to know whether such an effect also extends to the ORR activity in alkaline solution at room temperature, which has not yet been probed so far.…”

Electrical Conductivity and Oxygen Exchange Kinetics of La[sub 2]NiO[sub 4+δ] Thin Films Grown by Chemical Vapor Deposition

“…The La/Ni ratio optimization details, as well as the XRD patterns of the different phases obtained by varying the La/Ni ratio in an extreme range, are described elsewhere. 27 The deviation in the composition transfer between vapor and condensed phases is typical for MOCVD processes and occurs because each individual precursor has a different decomposition temperature which induces a different deposition yield for each element. The deposited lanthanum nickelates were nickel-rich compared with the injected precursor solution, as previously observed by Lane et 23 Increasing the deposition temperature gave rise to highly c-axis oriented La 2 NiO 4+␦ phases, showing for films deposited around 750°C the narrowest XRD peaks and the best surface morphology uniformity.…”