| Autor: |
Bodappa, Nataraju, Bouzidi, Sara, Liu, Xinran, Whittingham, Alexander W. H., Smith, Rodney D. L. |
| Zdroj: |
The Journal of Physical Chemistry - Part C; August 2023, Vol. 127 Issue: 34 p16870-16879, 10p |
| Abstrakt: |
Raman spectroscopic measurements on a series of perovskites as a function of the temperature and gaseous atmosphere reveal chemical reactions between CO2and La2CuO4that alter the thermal phase transitions and inhibit the synthesis of pristine La2CuO4. Variable temperature Raman spectra acquired under O2environments show that La2CuO4synthesized under ambient conditions undergoes not only the two previously documented phase transitions but also a loss of Raman vibrations at ca. 200 °C that we attribute to desorption of chemisorbed CO2. Samples heated to 700 °C and then cooled to room temperature under O2show a Raman spectrum with many fewer peaks; subsequent exposure to CO2at room temperature reveals a spontaneous surface reaction through an increased number of peaks in the spectrum. A subsequent heat ramp under CO2shows desorption of the additional CO2-related peaks, a ca. 50 °C change in temperature for the two thermal phase transitions, and signs of La2O2(CO3) formation at temperatures above 538 °C. The original La2CuO4spectrum is obtained only after heating in the presence of CO2, which suggests that synthesis under ambient conditions leads to incorporation of CO2into the structure. Partial substitution of Ni for Cu to obtain La2Cu0.9Ni0.1O4facilitates manipulation of oxygen vacancies in the lattice by heating in oxygen deficient or rich atmospheres but also prevents thermal phase transitions and inhibits direct reactions with CO2. We attribute both features to strengthened bonds between B-site cations and oxygen, which significantly alters chemical reactivity. We anticipate that in situvariable temperature Raman spectroscopy will be an effective tool for exploring chemical reactivity and guide synthetic protocol development for solid state materials. |
| Databáze: |
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