Self-limited kinetics of electron doping in correlated oxides
Jikun Chen (陈吉堃)1,#,*, You Zhou1,#, Srimanta Middey2, Jun Jiang1, Nuofu Chen3, Lidong Chen4,
５
Xun Shi4, Max Döbeli , Jian Shi,1+ Jacques Chakhalian2 and Shriram Ramanathan1
1School
of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts
02138, USA
2Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
3State Key Laboratory of Alternate Electrical Power System with Renewable Energy Source,
North China Electric Power University, Beijing 102206, , People’s Republic of China
4CAS Key Laboratory of Materials for Energy Conversion, Shanghai institute of Ceramics,
Chinese Academy of Sciences, Shanghai 200050, People’s Republic of China
5Laboratory
of Ion Beam Physics, ETH Zurich, Zurich 8093, Switzerland
# J. Chen and Y. Zhou equally contributed to this work
+ J. Shi is currently at Rensselaer Polytechnic Institute, Troy, NY 12180, USA.
*Corresponding author: Dr. Jikun Chen; jikunchen@seas.harvard.edu;
Supplemental Material
Experimental Details: Materials Synthesis
Several complex oxide systems have been studied in this work, and have been
synthesized in different laboratories or purchased from commercial vendors as
described in detail below. Specifically, SmNiO3 films were grown by co-sputtering
with Sm and Ni metal targets under 4:1 Ar/O2 at a pressure around 1 Pa on Si (100)
substrate at room temperature, followed by annealing at 1,500 psi pure O2 for 24
hours14. The NdNiO3 and EuNiO3 films have been grown by pulsed laser interval
deposition under 20 Pa O2 pressure on NdGaO3 substrate at a temperature range of
620C - 680 C, followed by annealing at growth temperature for 30 minutes under
oxygen pressure of 87 PaS1,S2. The La0.6Sr0.4MnO3 thin film was grown by pulsed laser
deposition (PLD) under 20 Pa O2 pressure on SrTiO3 (001) substrate at 650 CS3. The
LaNiO3 thin films were grown on LaAlO3 (100) substrate (Item Number:
LNO-LAO-101005S1) purchased from MTI Corporation. The Ca3Co4O9 thin film
was grown by PLD under 25 Pa O2 pressure on Si (100) substrate at 650 CS4.
Ca3Co4O9 is highly textured with its c axis perpendicular to the Si (100)S5. As a result,
there is no strong in-plane anisotropy in the electrical measurements. The
SrNb0.4Ti0.6O3 thin film is grown by PLD under 1 Pa O2 pressure on LaAlO3 (100)
substrate at 680 C. The cation composition of representative as-grown thin films was
confirmed by Rutherford backscattering (RBS) at the Ion Beam Laboratory in ETH
Zurich (data not shown). The film thicknesses are in the range of 100nm for the
various samples, with the exception of EuNiO3 and NdNiO3 that are nearly 20nm
thick.
For the hydrogenation process, Pt electrodes were patterned on all samples in an
identical manner by sputtering under 10 Pa Ar pressure at room temperature. The time
dependent evolution in resistance of the oxide thin films during the hydrogenation
processes was performed inside a custom-designed probe station with environmental
control as described in ref. 14. The 5% H2/Ar, regulated at 150 sccm, were introduced
into the chamber for the hydrogenation of all the investigated thin film samples.
Electrical measurements were performed on samples under identical conditions and
data reported here are representative for all materials studied. X-ray photoelectron
spectroscopy (XPS) measurements were performed by using a K-Alpha Thermo
Scientific XPS system.
References:
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Liu, M. Kareev, B. Gray, J. W. Kim, P. Ryan, B. Dabrowski, J. W. Freeland and J. Chakhalian,
Appl. Phys. Lett. 96, 233110 (2010)
S2D.
Meyers, S. Middey, M. Kareev, M. van Veenendaal, E. J. Moon, B. A. Gray, J. Liu, J. W.
Freeland and J. Chakhalian, Phys. Rev. B 88, 075116 (2013)
S3J.
Chen, A. Palla-Papavlu, Y. Li, L. Chen, X. Shi, M. Döbeli, D. Stender, S. Populoh, W. Xie, A.
Weidenkaff, C. W. Schneider, A. Wokaun, and T. Lippert, Appl. Phys. Lett. 104, 231907 (2014)
S4J.
Chen, M. Döbeli, D. Stender, K. Conder, A. Wokaun, C. W. Schneider and T. Lippert, Appl.
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F. Hu, W. D. Si, E. Sutter, and Q. Li, Appl. Phys. Lett. 86, 82103 (2005).
Figure S1. (a) Illustration of the patterned Pt bars on the surface of the ReNiO3 thin
films that acts as catalyst during hydrogenation process. (b) Optical image of the
hydrogenated SmNiO3 or LaNiO3 (left) as compared to pristine samples (right). A
change in color is observed near the platinized region of the SmNiO3 after the
hydrogenation process at 150 °C, while no change has been observed for the LaNiO3
before and after the same hydrogenation process. The color change in the former case
is related to the change in effective band gap upon hydrogenation.
Figure S2. Variation in resistance of La0.6Sr0.4MnO3 as a function of time under 5%
hydrogen atmosphere in presence of Pt electrodes. The blue region represents
exposure under 5% H2, while the white region represents air. Sr is drawn in light
green, La in dark green, Mn in pink, oxygen atoms are omitted in the MnO6
octahedra.
Figure S3. Variation in resistance when platinized (a) samarium nickelate or (b)
SrNb0.4Ti0.6O3 is exposed to hydrogen at room temperature (RT black curve) or
elevated temperature of 90 °C (blue curve) or 150 °C (red curve). The blue region
represents exposure under 5% H2, while the white regions represents air. We can see
that increasing the temperature speeds up the hydrogenation process. The process is
reversible if the samples are annealed in air at comparable temperatures. On the other
hand, if the sample is cooled down to room temperature after hydrogenation, the high
resistance state can be sustained in ambient conditions. Stability of the hydrogenated
state of (c) samarium nickelate or (d) SrNb0.4Ti0.6O3 at room temperature in air. The
samples were annealed in 5%H2/Ar either at room temperature or 150 °C. For 150 °C
annealed samples, the sample was cooled down to room temperature in same
hydrogen environment so that the hydrogenated sate is preserved. Then the samples
were exposed to air and resistance-time evolution is monitored. The samarium
nickelate or SrNb0.4Ti0.6O3 hydrogenated at 150 °C shows a stabilized R∞ in air at
room temperature. In contrast, the resistance for samples hydrogenated at room
temperature recovers to their initial value under exposure in air indicating
metastability.
Figure S4. (a) Variation in resistance when platinized lanthanum nickelate is exposed
to hydrogen at 150 °C. A larger R∞/R0 ratio is observed at 150 °C as compared to
room temperature as shown in Figure 1c. (b) Stability in air and room temperature of
the resistance of the hydrogenated lanthanum nickelate annealed at 150 °C. The blue
region represents exposure under 5% H2, while the white regions represents air. The
hydrogenated lanthanum nickelate at 150 °C shows a slight decrease in resistivity
when exposed to air at room temperature, and the stabilized R∞/R0 ratio is around 10.
Oxide
R∞/R0
Kex (s-1)
Ca3Co4O9
1.3
6.2 x 10-2
La0.6Sr0.4MnO3
1.1
1.6 x 10-3
SrNb0.4Ti0.6O3
0.5
1.8 x 10-2
Table S1. The resistance change ratio R∞/R0 and kinetic constant Kex upon 5%
hydrogen exposure for Ca3Co4O9, La0.6Sr0.4MnO3 and SrNb0.4Ti0.6O3. As compared to
those for ReNiO3 (Re=Eu, Sm or Nd), much smaller resistance change ratio is
observed for the three conducting oxides.
Figure S5. Kinetic constant Kex for the de-hydrogenation process in air at room
temperature for various oxides studied in this work.
Figure S6. Representative X-ray diffraction pattern taken from (a) platinized EuNiO3
film grown on NdGaO3 (110) substrate and (b) LaNiO3 grown on LaAlO3 (100)
substrate before and after hydrogenation process. As labeled film peak in (a) is the
(002) peak of EuNiO3 while the substrate peak is the (110) peak of NdGaO3 (Kα1 and
Kα2 are not separated). As labeled film peak in (b) is the (200) peak of LaNiO3 while
the substrate peak is the (200) peak of LaAlO3 (Kα1 and Kα2 are not separated). There
is no new crystal phase or drastic structural symmetry changes observed upon
hydrogenation. A slightly reduced intensity of the thin film peak as compared to the
substrate was seen after the hydrogenation for EuNiO3 which also shows the
maximum change in resistance. The relative intensity of the EuNiO3 film peak
reduced after hydrogen annealing, while no significant changes were observed for
LaNiO3 under the same process indicating absence of any new structural phase
formation. These results are in agreement with our understanding that the hydrogen
diffusion and incorporation is more effective for the meta-stable EuNiO3 or SmNiO3
with a more positive G at ambient pressure, as compared to the stable LaNiO3 as
well as other conducting oxides such as Ca3Co4O9, La0.6Sr0.4MnO3 and SrNb0.4Ti0.6O3