Mykola Abramchuk

Layered honeycomb iridates receive significant attention in the materials chemistry and physics fields due to the relevance of their crystal structures to the Kitaev model of a quantum spin liquid (QSL). In quest of liquid‐like magnetic ground state signatures, first‐generation alkali metal iridates A₂IrO₃ ≡ A₃[AIr₂]O₆ (A = Li, Na) and second‐generation iridates T₃[AIr₂]O₆ (T = Cu, Ag, H) are developed. T₃[AIr₂]O₆ is synthesized from A₃[AIr₂]O₆ via metathesis reactions replacing alkali ions located between honeycomb layers. Herein, the next level of chemical and structural complexity is introduced by synthesizing the honeycomb iridate, Cu₃ZnIr₂O₆, in which alkali ions between and within the honeycomb layers are both selectively exchanged with two different transition metals. Analysis of powder X‐Ray diffraction data reveals corrugation of the honeycomb layers in Cu₃ZnIr₂O₆ that hinders complete magnetic frustration and results in a spin glass behavior observed from magnetization and specific heat data. Thus, Cu₃ZnIr₂O₆ represents yet another model, which broadens understanding of intricate relationships between intralayer distortions and magnetism of prospective Kitaev QSL compounds.

We apply high-temperature oxide melt solution calorimetry to assess the thermodynamic properties of the material Li_1+xAl_xTi_2–x(PO₄)₃, which has been broadly recognized as one of the best Li-ion-conducting solid electrolytes of the NASICON family. The experimental results reveal large exothermic enthalpies of formation from binary oxides (ΔH_f,ox^°) and elements (ΔH_f,el^°) for all compositions in the range 0 ≤ x ≤ 0.5. This indicates substantial stability of Li_1+xAl_xTi_2–x(PO₄)₃, driven by thermodynamics and not just kinetics, during long-term battery operation. The stability increases with increasing Al³⁺ content. Furthermore, the dependence of the formation enthalpy on the Al³⁺ content shows a change in behavior at x = 0.3, a composition near which the Li⁺ conductivity reaches the highest values. The strong correlation among thermodynamic stability, ionic transport, and clustering is a general phenomenon in ionic conductors that is independent of the crystal structure as well as the type of charge carrier. Therefore, the thermodynamic results can serve as guidelines for the selection of compositions with potentially the highest Li⁺ conductivity among different NASICON-type series with variable dopant contents.

Van der Waals (VdW) materials have opened new directions in the study of low dimensional magnetism. A largely unexplored arena is the intrinsic tuning of VdW magnets toward new ground states. Chromium trihalides provided the first such example with a change of interlayer magnetic coupling emerging upon exfoliation. Here, we take a different approach to engineer previously unknown ground states, not by exfoliation, but by tuning the spin-orbit coupling (SOC) of the nonmagnetic ligand atoms (Cl, Br, I). We synthesize a three-halide series, CrCl_{3 − x − y}Br_xI_y, and map their magnetic properties as a function of Cl, Br, and I content. The resulting triangular phase diagrams unveil a frustrated regime near CrCl₃. First-principles calculations confirm that the frustration is driven by a competition between the chromium and halide SOCs. Furthermore, we reveal a field-induced change of interlayer coupling in the bulk of CrCl_{3 − x − y}Br_xI_y crystals at the same field as in the exfoliation experiments.

Defect fluorite yttrium niobate Y ₃ NbO ₇ and pyrochlore yttrium titanate Y ₂ Ti ₂ O ₇ solid solutions are single-phase oxygen ion- and proton-conducting materials.

We report on an ultralow probe-power transient grating apparatus with probing based on a laser diode pulser, a digital delay generator, and a data acquisition card. The electronic triggering of the diode pulser permits stroboscopic measurement of arbitrarily slow laser-induced dynamics using pulses of probe light with average power ∼ 5 n W , significantly lower than what is currently used by continuous wave measurement. The proposed method also allows for flexibility in selection of the probe wavelength limited only by availability of low threshold current laser diodes. Examples of impulsive stimulated thermal scattering measurements are presented on liquid isopropanol, single crystal solid C r C l 3 , and a thin film of Cu vapor deposited on a Si substrate, demonstrating the flexibility of the technique.