Ilmenite-Type Ca$_x$IrO$_3$ via Topochemical Ion Exchange: Stacking Faults and Low-Temperature Magnetic Anomaly
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| Formato: | Preprint |
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2026
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| _version_ | 1866912906590814208 |
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| author | Kira, Haruki Haraguchi, Yuya Yokoshima, Wataru Nishio-Hamane, Daisuke Katori, Hiroko Aruga |
| author_facet | Kira, Haruki Haraguchi, Yuya Yokoshima, Wataru Nishio-Hamane, Daisuke Katori, Hiroko Aruga |
| contents | We report the synthesis of an ilmenite-type polymorph of Ca$_x$IrO$_3$ distinct from the known post-perovskite and perovskite phases, via low-temperature topochemical Ca$^{2+}$/2Na$^+$ exchange from Na$_2$IrO$_3$. Powder X-ray diffraction is indexable in $R\bar{3}$, and whole pattern modelling that includes layer glide faults indicates that the selective broadening can be captured by a first order Markov stacking description based on stochastic switching between two symmetry equivalent lateral stacking steps, with explicit model dependence and an uncertainty of at least several percent. A freezing-like bulk magnetic anomaly is suggested at $T^* \sim 25$ K (defined by the onset of a ZFC/FC bifurcation at $μ_{0}H = 10$ mT), accompanied by a broad heat capacity feature and Curie-Weiss behavior with a large negative Weiss temperature of $θ_W \sim -98$ K. The effective moment $μ_{\rm eff} = 1.68 μ_{\rm B}$ per Ir is consistent with $J_{\rm eff} = 1/2$ for an Ir$^{4+}$. SEM-EDX suggests an A-site content below unity (Ca/Ir $<$ 1); accordingly, we describe the ion-exchanged product using the nonstoichiometric formula Ca$_x$IrO$_3$. These results identify ilmenite-type CaIrO$_3$ as a honeycomb iridate in which stacking disorder can be quantified (with caveats regarding model and instrument correlations) and related to its low-temperature magnetic behavior. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2602_14377 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Ilmenite-Type Ca$_x$IrO$_3$ via Topochemical Ion Exchange: Stacking Faults and Low-Temperature Magnetic Anomaly Kira, Haruki Haraguchi, Yuya Yokoshima, Wataru Nishio-Hamane, Daisuke Katori, Hiroko Aruga Materials Science Strongly Correlated Electrons We report the synthesis of an ilmenite-type polymorph of Ca$_x$IrO$_3$ distinct from the known post-perovskite and perovskite phases, via low-temperature topochemical Ca$^{2+}$/2Na$^+$ exchange from Na$_2$IrO$_3$. Powder X-ray diffraction is indexable in $R\bar{3}$, and whole pattern modelling that includes layer glide faults indicates that the selective broadening can be captured by a first order Markov stacking description based on stochastic switching between two symmetry equivalent lateral stacking steps, with explicit model dependence and an uncertainty of at least several percent. A freezing-like bulk magnetic anomaly is suggested at $T^* \sim 25$ K (defined by the onset of a ZFC/FC bifurcation at $μ_{0}H = 10$ mT), accompanied by a broad heat capacity feature and Curie-Weiss behavior with a large negative Weiss temperature of $θ_W \sim -98$ K. The effective moment $μ_{\rm eff} = 1.68 μ_{\rm B}$ per Ir is consistent with $J_{\rm eff} = 1/2$ for an Ir$^{4+}$. SEM-EDX suggests an A-site content below unity (Ca/Ir $<$ 1); accordingly, we describe the ion-exchanged product using the nonstoichiometric formula Ca$_x$IrO$_3$. These results identify ilmenite-type CaIrO$_3$ as a honeycomb iridate in which stacking disorder can be quantified (with caveats regarding model and instrument correlations) and related to its low-temperature magnetic behavior. |
| title | Ilmenite-Type Ca$_x$IrO$_3$ via Topochemical Ion Exchange: Stacking Faults and Low-Temperature Magnetic Anomaly |
| topic | Materials Science Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2602.14377 |