BCMaterials Fortnightly Seminars #23

“Lattice anomalies at the ferroelectric and magnetic transitions in cycloidal Mn_0.95Co_0.05WO₄ and conical Mn_0.80Co_0.20WO₄ multiferroics” 

Irene Urcelay Olabarria

(BCMaterials)

Different types of subtle lattice anomalies (Dl/l ∼ 10⁻⁵) are reported in the multiferroic Mn_1−xCo_xWO₄ (x = 0.05 and 0.20) compounds coinciding with the successive magnetic transitions below 30 K. Clearly different magnetoelastic effects at the ferroelectric transition (T_FE = T_N2) were observed for Mn_0.95Co_0.05WO₄ (single-k pure cycloidal order below T_FE) andMn_0.80Co_0.20WO₄ (double-k conical order below T_FE). The different lattice evolution across T_FE results from a distinct relative orientation of the magnetic easy axis and the spiral plane. Whereas both are parallel in Mn_0.95Co_0.05WO₄, the spiral plane is perpendicular to the easy axis in Mn_0.80Co_0.20WO₄.  

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“Polyanionic Materials as Cathodes for Na-ion Batteries” 

Verónica Palomares

(UPV/EHU)

Na-ion batteries are considered one of the most promising energy storage systems for a near post-lithium future. In order to make these batteries come true, every battery component (electrodes, electrolytes, separator) must be optimized to obtain the best possible performance. Research work on polyanionic structures as cathode materials has been intense in the last 5 years. Many reasons support this fact: they possess high operating voltages (due to the inductive effect), there are several known structures that could bear Na ion extraction/insertion, and there exists previous knowledge from Li-ion batteries on some of them. This contribution gathers the main polyanionic compounds signaled as possible cathodes for Na-ion batteries, with the most relevant advances on them. These materials will be analyzed in terms of energy density (operating voltage and specific capacity), easiness or preparation, morphology affecting electrochemical performance, the need of conductive coatings… This way a general view of the different materials that can be chosen as electrode for a Na-ion battery will be given, pointing out which could be the next steps involved in the research of this type of materials.