Negative thermal expansion of Ca<sub>2</sub>RuO<sub>4</sub> with oxygen vacancies

Negative thermal expansion of Ca₂RuO₄ with oxygen vacancies

Xu Sen¹, Hu Yangming¹, Liang Yuan^{2, †}, Shi Chenfei³, Su Yuling³, Guo Juan¹, Gao Qilong¹, Chao Mingju¹, Liang Erjun^{1, ‡}

(a) XPS analysis for the Ru 4d orbitals of the samples prepared with O₂/Ar ratios of 0.5%, 1.0%, 1.5%, and 2.0% and in ambient atmosphere conditions, red: Ru⁺⁵, yellow: Ru⁺⁴, green: Ru⁺³. (b)–(d) Rietveld analysis of the SXRD patterns for (b) Ca₂RO_3.87, (c) Ca₂RO_3.73 and (d) Ca₂RO_4.09.