Transition metal oxides containing nickel species in oxidation states higher than 3+ often exhibit high catalytic activity, which makes them promising for applications as advanced electrocatalysts for water splitting and fuel cells. Here, we examine the structure and properties of $\mathrm{BaNi}{\mathrm{O}}_3$ (BNO) thin films, containing formally ${\mathrm{Ni}}^{4+}$, grown on $\mathrm{SrTi}{\mathrm{O}}_3$ (111) substrates using oxygen-plasma–assisted molecular beam epitaxy. X-ray diffraction and scanning transmission electron microscopy measurements reveal that BNO films have a hexagonal structure with $c$- and $a$-axes of mixed textures showing epitaxial relationships BNO $\left(0001\right)\parallel \mathrm{SrTi}{\mathrm{O}}_3$ (111) and BNO $\left(10\overline{1}0\right)\parallel \mathrm{SrTi}{\mathrm{O}}_3$ (111), respectively. The formation of the $a$-axis texture is dominant due to the smaller lattice mismatch with the substrate. Density functional theory calculations confirm that the hexagonal BNO film with the $a$-axis texture is energetically more favorable than the competing $c$-axis texture. Detailed spectroscopy data analysis indicates that hexagonal BNO films contain mixtures of ${\mathrm{Ni}}^{2+}, {\mathrm{Ni}}^{3+}$, and ${\mathrm{Ni}}^{4+}$ species, with ${\mathrm{Ni}}^{4+}$ being dominant. Our study provides insights into stabilizing ${\mathrm{Ni}}^{4+}$ in complex oxides, which is important for further exploration of the potential of materials containing ${\mathrm{Ni}}^{4+}$.

We report confocal microscopy experiments of electric-field-driven crystal-crystal transformations in microgel colloids with varying particle softness. The transformation kinetics are well described by phenomenological nucleation and growth theory. Using a spatial projection formalism, we determine local susceptibilities to affine shear deformation and nonaffine defect formation in the parent crystal. Curiously, the softer particles have lower shear strain susceptibility, while nonaffine susceptibility and phenomenological growth coefficients depend nonmonotonically on particle softness.

Manganese, showing stable oxidation states spanning from +2 to +7, gives rise to a variety of oxides ($\mathrm{Mn}{\mathrm{O}}_x$) whose exploitation in several technological fields, such as energy conversion and storage, catalysis, sensing, and environmental and biomedical engineering, is highly promising. Nevertheless, the chemical complexity and the structural richness of $\mathrm{Mn}{\mathrm{O}}_x\text{—}\mathrm{involving}$ mixed-valence and metastable species—make the correct identification by Raman spectroscopy challenging, further complicated by the laser sensitivity, poor Raman activity, and conflicting literature scenario. Moreover, a careful optimization of the material in terms of phase, structure, and morphology is highly desirable in view of the final application, where precise control over the materials properties is essential. In this paper, we discuss the capability of room-temperature pulsed laser deposition (PLD) followed by postdeposition thermal treatments to successfully grow engineered and pure $\mathrm{Mn}{\mathrm{O}}_x$ thin films, whose phase and morphology at the nanoscale can be totally decoupled and independently optimized. The detailed Raman characterization of these films enabled a clear identification of specific $\mathrm{Mn}{\mathrm{O}}_x$ phases and poses the basis for the rationale of the $\mathrm{Mn}{\mathrm{O}}_x$ Raman spectra. Starting from the same MnO PLD target, we obtained five different $\mathrm{Mn}{\mathrm{O}}_x$ phases (i.e., MnO, ${\mathrm{Mn}}_3{\mathrm{O}}_4, {\mathrm{Mn}}_2{\mathrm{O}}_3$, amorphous $\mathrm{Mn}{\mathrm{O}}_2$, and $\alpha \text{−}\mathrm{Mn}{\mathrm{O}}_2$) with tailored and tunable degree of porosity and crystallinity, by modulating process parameters like the ${\mathrm{O}}_2$ deposition partial pressure (vacuum to 100 Pa), the type of substrate, and the annealing temperature ($300-900{}^{\circ }\mathrm{C}$) and atmosphere (air/vacuum). The Raman spectroscopy reliability of the $\mathrm{Mn}{\mathrm{O}}_x$ phase assignment was assessed by thoroughly investigating the impact of the exciting laser power, and it was further validated by energy-dispersive x-ray spectroscopy, x-ray photoemission spectroscopy, and x-ray diffraction, providing additional insight into the compositional properties and the crystalline structure.

Mechanical response of single-crystal ${\mathrm{CsPbI}}_3, {\mathrm{CsPbBr}}_3, {\mathrm{CsPbIBr}}_2$, and ${\mathrm{CsPbI}}_2\mathrm{Br}$ is investigated under uniaxial tension and compression using molecular dynamics (MD) simulations. Stress-strain curves for these metal-halide perovskites are determined and mechanisms that strengthen and weaken them under plastic deformation are revealed. Our study finds the mechanical response of these crystals to differ considerably under uniaxial tension and compression. While ${\mathrm{CsPbI}}_3$ and ${\mathrm{CsPbBr}}_3$ exhibit a smooth elastic to plastic transition under uniaxial tension, distinct elastic and plastic regimes are observed under uniaxial compression. Only ${\mathrm{CsPbI}}_3$ is noted to exhibit strain hardening under uniaxial compression, which is deciphered to arise from generation of defects in the plastic regime. These defects, which take the form of deformation-induced distortion of the Pb-I octahedra, are shown to manifest as superlattice reflections in optical diffraction patterns derived from fast Fourier transform analysis of MD simulations. While a perfectly plastic postyield response is observed in ${\mathrm{CsPbIBr}}_2$ and ${\mathrm{CsPbI}}_2\mathrm{Br}$ under tension, a monotonic reduction in stress occurs after yielding under compression. Formation and growth of bands of high von Mises shear strain is revealed as an important plastic deformation mechanism in ${\mathrm{CsPbIBr}}_2$ and ${\mathrm{CsPbI}}_2\mathrm{Br}$ under uniaxial tension and compression. The evolution of defect microstructure with strain discussed here is expected to provide insights into plausible mechanisms that operate in metal-halide perovskites under experiments such as nanoindentation, while the defect-induced strengthening demonstrated here points to the possibility of fabricating robust perovskite films by engineering defects into the material.

A phase of silver iodate, $\gamma \text{−}{\mathrm{AgIO}}_3$, has been obtained at ambient temperature by compressing $\alpha \text{−}{\mathrm{AgIO}}_3$ to 1.60(5) GPa. The $\gamma \text{−}{\mathrm{AgIO}}_3$ crystal structure was identified via Rietveld refinement of high-pressure powder synchrotron x-ray diffraction. The $\gamma \text{−}{\mathrm{AgIO}}_3$ reflections were indexed to an orthorhombic lattice (Pbca) with unit-cell dimensions of $a=7.2945\left(12\right), b=15.0013\left(24\right), c=5.3904\left(9\right)\AA$, and $V=589.85\left(29\right){\AA }^3$ at 2.20(5) GPa. Density-functional theory calculations predict that $\gamma \text{−}{\mathrm{AgIO}}_3$ is more stable than $\alpha \text{−}{\mathrm{AgIO}}_3$ above 0.15 GPa. The $\alpha \to \gamma$-phase transition is characterized by a decrease in the volume per formula unit of approximately 2% and it is reversible on decompression. Single-crystal optical-absorption measurements and density-functional theory calculations reveal the electronic band gap to decrease monotonically with increasing pressure in both α and γ phases, however the $\alpha \to \gamma$-phase transition (indirect $\to$ indirect) is characterized by an abrupt band-gap energy increase of approximately $+0.18\mathrm{eV}$. This pressure induced band-gap evolution is rationalized based on the I-O bond lengths. The γ phase may correspond to an intermediate step between the previously known α and β phases.

Niobium with its highest transition temperature among all elemental superconductors has become a favorable substrate for realizing well-defined low-dimensional magnet-superconductor hybrid systems exhibiting novel types of exotic electronic states such as Majorana zero-energy modes. While a preparation procedure for obtaining atomically clean Nb(110) substrates has previously been reported, a suitable preparation method for clean Nb(111) surfaces is still lacking. Here, we report a recipe for cleaning Nb(111) surfaces based on an atomic hydrogen treatment followed by short flashes to elevated temperatures. The atomic surface structure of clean nonreconstructed Nb(111) is investigated by high-resolution scanning tunneling microscopy, as well as a surface reconstruction with a reduced atom density compared to the (111) plane of a bcc crystal resulting from a surface premelting at high annealing temperatures.

Achieving superconductivity at room temperature could lead to substantial advancements in industry and technology. Recently, a compound known as Cu-doped lead-apatite, ${\mathrm{Pb}}_{10-x}{\mathrm{Cu}}_x{\left(\mathrm{P}{\mathrm{O}}_4\right)}_6\mathrm{O} \left(0.9<x<1.1\right)$, referred to as “LK-99,” has been reported to exhibit unusual electrical and magnetic behaviors that appear to resemble a superconducting transition above room temperature. In this work we collected multiphase samples containing the nominal ${\mathrm{Pb}}_{10-x}{\mathrm{Cu}}_x{\left(\mathrm{P}{\mathrm{O}}_4\right)}_6\mathrm{O}$ phase (no superconductivity was observed in our measured samples), synthesized by three independent groups, and studied their chemical, magnetic, and electrical properties at the microscale to overcome difficulties in bulk measurements. Through the utilization of optical, scanning electron, atomic force, and scanning diamond nitrogen-vacancy microscopy techniques, we were able to establish a link between local magnetic properties and specific microscale chemical phases. Our findings indicate that while the ${\mathrm{Pb}}_{10-x}{\mathrm{Cu}}_x{\left(\mathrm{P}{\mathrm{O}}_4\right)}_6\mathrm{O}$ phase seems to have a mixed magnetism contribution, a significant fraction of the diamagnetic response can be attributed to Cu-rich regions (e.g., ${\mathrm{Cu}}_2\mathrm{S}$ derived from a reagent used in the synthesis). Additionally, our electrical measurements reveal the phenomenon of current path switch and a change in resistance states of ${\mathrm{Cu}}_2\mathrm{S}$. This provides a potential explanation for the electrical behavior observed in compounds related to ${\mathrm{Pb}}_{10-x}{\mathrm{Cu}}_x{\left(\mathrm{P}{\mathrm{O}}_4\right)}_6\mathrm{O}$.

${\mathrm{LaInO}}_3$ is a lattice-matched barrier material for the confinement of two-dimensional electron gases at the interface with the perovskite ${\mathrm{BaSnO}}_3$, which is known for its high room-temperature electron mobility. Here, we report the adsorption-controlled growth of epitaxial ${\mathrm{LaInO}}_3$ by molecular beam epitaxy (MBE), a growth method that has demonstrated the highest electron mobilities in ${\mathrm{SrTiO}}_3$ and ${\mathrm{BaSnO}}_3$ thin films. The adsorption-controlled growth was monitored using line-of-sight quadrupole mass spectrometry. In a thermodynamics of MBE diagram, the experimental growth window was found to be significantly narrower than the theoretically predicted one. We found the critical thickness for strain relaxation of the ${\mathrm{LaInO}}_3$ layer on ${\mathrm{DyScO}}_3$(110) substrates (lattice mismatch $\approx -4\%$) to be 1 nm using in situ reflection high-energy electron diffraction analysis. The substrate and film possess an orthorhombic crystal structure which can be approximated by a pseudocubic lattice. X-ray-diffraction analysis revealed the pseudocube-on-pseudocube epitaxial relationship of the ${\mathrm{LaInO}}_3$ films to the ${\mathrm{DyScO}}_3$ substrates. This relation was confirmed by transmission electron microscopy, which further resolved the presence of rotational orthorhombic domains, the majority of which have a $c$ axis that coincides with that of the substrate. Raman spectroscopy further confirmed the presence of a ${\mathrm{LaInO}}_3$ layer. Our findings provide the missing building block for the realization of two-dimensional electron gases with high room-temperature electron mobilities at the MBE-grown heterointerface with ${\mathrm{BaSnO}}_3$.

Doping hydrogen in correlated oxides is a promising way to control the materials functionalities. With in situ measurements of the resistance and hydrogen concentration by a nuclear reaction analysis, we have derived the detailed relation between the resistance and hydrogen concentration ($x$) for $R{\mathrm{NiO}}_3{\mathrm{H}}_x$ ($R=\text{Sm}$, Nd, and La), which reveal a clear resistance jump at a certain concentration. Taking account of the spatial distribution of hydrogen in both in-plane and depth directions, we have clarified that an insulating state is realized at $x=0.5$ and another insulating state is formed at $x=1$. The electronic mechanisms for the two states are proposed in terms of Mott phases.

Due to the focus on their high reactivity, the mechanical properties of Al/Ni multilayer nanofoils have not yet been investigated extensively. However, as Al/Ni multilayers are potentially going to be integrated into various applications, it is also important to understand their mechanical properties. In this paper, molecular dynamics simulations are used to investigate the mechanical properties, namely hardness and Young's modulus, of Al/Ni multilayers via nanoindentation. Furthermore, the results are contextualized by comparison with simulated uniform uniaxial compression. The following essential features have been investigated: the influence of the grain orientation, of a naturally occurring premixed interlayer at the Al-Ni interface, and ultimately of the bilayer height on the mechanical properties is explored. An inverse Hall-Petch effect is observed, meaning that both hardness and Young's modulus decrease with decreasing bilayer height. At the same time, the modulus-to-hardness ratio increases with decreasing bilayer height. Premixed interlayers only show an effect on the mechanical properties for very small bilayer heights, where they make up a clear majority of volume fraction of the full system. The mechanical properties obtained from nanoindentation are in good agreement with those obtained from uniaxial compression. Insights from this study might be transferred to other fcc/fcc multilayer systems.

The shandite compounds (chemical formula $M_3{A}_2{B}_2$) with a kagome structure have recently attracted significant interest due to their novel quantum topological states, such as the ferromagnetic Weyl semimetal in ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$, and endless Dirac nodal lines in ${\mathrm{Ni}}_3{\mathrm{In}}_2{\mathrm{S}}_2$. In this study, we successfully grew ${\mathrm{Ni}}_3{\mathrm{In}}_2{\mathrm{Se}}_2$ crystal, a sister compound of ${\mathrm{Ni}}_3{\mathrm{In}}_2{\mathrm{S}}_2$, and investigated its possible topological state and physical properties. Temperature-dependent resistivity measurements of ${\mathrm{Ni}}_3{\mathrm{In}}_2{\mathrm{Se}}_2$ demonstrate metallic behavior, which can be accurately described by the Bloch-Grüneisen model. This suggests that electron-phonon scattering dominates the electrical transport in ${\mathrm{Ni}}_3{\mathrm{In}}_2{\mathrm{Se}}_2$, which is also supported by Kohler's rule analysis. The Hall resistivity characterizations reveal the coexistence of both electrons and holes in ${\mathrm{Ni}}_3{\mathrm{In}}_2{\mathrm{Se}}_2$. Meanwhile, systematic analysis of the de Haas–van Alphen oscillation suggests that there are three Fermi pockets in ${\mathrm{Ni}}_3{\mathrm{In}}_2{\mathrm{Se}}_2$, and extracted Berry phases are null. Combining first-principles calculation and experimental analysis, we propose that ${\mathrm{Ni}}_3{\mathrm{In}}_2{\mathrm{Se}}_2$ is a multiband and topologically trivial semimetal. The evolution from Dirac nodal lines in ${\mathrm{Ni}}_3{\mathrm{In}}_2{\mathrm{S}}_2$ to trivial topology in ${\mathrm{Ni}}_3{\mathrm{In}}_2{\mathrm{Se}}_2$ may be attributed to the significantly enhanced spin-orbit coupling (SOC) in ${\mathrm{Ni}}_3{\mathrm{In}}_2{\mathrm{Se}}_2$. The SOC effect also leads to a small-angle canting along the $c$ axis of antiferromagnetically aligned spins in the $ab$ plane. Our work provides valuable insights into the quantum states of shandite compounds with a kagome structure.

Geometrically frustrated structures, combined with competing exchange interactions that have different magnitudes, are known ingredients for achieving exotic properties. Herein, we studied detailed structural, magnetic, thermal (specific heat), magnetodielectric, and magnetic exchange bias properties of a mixed $3d\text{−}4d$ spinel oxide with composition ${\mathrm{CoFeRhO}}_4$. Detailed magnetization, heat capacity, and neutron powder diffraction studies highlight long-range ferrimagnetic ordering with an onset at 355 K. The magnetic structure is established using a ferrimagnetic model (collinear type) that has a propagation vector $k=0$, 0, and 0. The magnetodielectric effect appears below the magnetic ordering temperature, and the exchange bias (EB) effect is observed in field-cooled conditions below 355 K. The magnetodielectric coupling in ${\mathrm{CoFeRhO}}_4$ originates due to the frustration in the structure, collinear ferrimagnetic ordering, and uncompensated magnetic moments. The unidirectional anisotropy resulting from the uncompensated magnetic moments causes the room-temperature exchange bias effect. Remarkably, the appearance of technologically important properties (ferromagnetism, magnetodielectric effect, and EB) at room temperature in ${\mathrm{CoFeRhO}}_4$ indicates its potential use in sensors or spintronics.

The effects of doping on the electronic evolution of the Mott insulating state have been extensively studied in efforts to understand mechanisms of emergent quantum phases of materials. The study of these effects becomes ever more intriguing in the presence of entanglement between spin and orbital degrees of freedom. Here, we present a comprehensive investigation of charge doping in the double perovskite ${\mathrm{Ba}}_2{\mathrm{NaOsO}}_6$, a complex Mott insulator where such entanglement plays an important role. We establish that the insulating magnetic ground state evolves from canted antiferromagnet (cAFM) [Lu et al., Nat. Commun. 8, 14407 (2017)] to Néel order for dopant levels exceeding $\approx 10\%$. Furthermore, we determine that a broken local point symmetry (BLPS) phase, precursor to the magnetically ordered state, occupies an extended portion of the ($H-T$) phase diagram with increased doping. This finding reveals that the breaking of the local cubic symmetry is driven by a multipolar order, most likely of the antiferro-quadrupolar type [Khaliullin et al., Phys. Rev. Res. 3, 033163 (2021); Churchill and Kee, Phys. Rev. B 105, 014438 (2022)]. Future dynamical measurements will be instrumental in determination of the precise nature of the identified multipolar order.

We report on the temperature dependence of selective phonon scattering and magnetization switching in $\left(\mathrm{GdSm}\right)\mathrm{Cr}{\mathrm{O}}_3$ perovskites. Thermal evolution of key phonon modes $A_{1g}\left(6/5/3\right)$ and their anomalous change across the antiferromagnetic (AFM) Néel temperature $\left(T_{\mathrm{N}}\sim 202\mathrm{K}\right)$ endorses the strong spin-phonon coupling in the investigated system. Such changes have been identified in consonance with the vibrational spectrum of trivalent Gd and Cr along with antistretching/bending of $\mathrm{Gd}/\mathrm{Sm}\text{−}{\mathrm{O}}_{12}$ polyhedra and $\mathrm{Cr}{\mathrm{O}}_6$ octahedra. Further, we find the emergence of many interesting features, such as thermomagnetic irreversibilities of the magnetization, significant enhancement of the ordering temperatures (up to 202 K), and multiple magnetization switching below $T_{\mathrm{N}}$ (9.7–85 K) upon the substitution of Sm at Gd sites. We find the presence of kinetic arrest of magnetic phases $[{\mathrm{\Gamma }}_4\left(G_x,A_y,F_Z;F_R\right)$ and ${\mathrm{\Gamma }}_2$ ($F_x, C_y, G_z$; $F_x^R, C_y^R$)] along with the presence of nonequilibrium frozen AFM and ferromagnetic clusters ($<30$ K with 70.7% frozen fraction), indicating the presence of a magnetic glassy state which assists the ${\mathrm{\Gamma }}_4\text{-to-}{\mathrm{\Gamma }}_2$ phase transition and supports the phase-coexistence nature of the $\left(\mathrm{GdSm}\right)\mathrm{Cr}{\mathrm{O}}_3$ perovskites. Interestingly, Sm moments order across 6.82 K ($T_{\mathrm{N}}^{\mathrm{Sm}}$), giving rise to yet another phase transition: ${\mathrm{\Gamma }}_{26}\left(C_x,G_y,C_x;C_x^R,A_y^R,F_z^R\right)/{\mathrm{\Gamma }}_{27}\left(F_x,C_y,G_z;F_x^R,C_y^R,G_z^R\right)$. On the other hand, field-dependent $\left(100\mathrm{Oe}\le H_{\mathrm{DC}}\le 600\mathrm{Oe}\right)$ bipolar switching of magnetization $\left(-7.8/+2.1/-12/+16\mathrm{emu}/\mathrm{mol}\right)$ at different temperatures below $T_{\mathrm{N}}$ under different measurement protocols makes the investigated system a suitable candidate for the magnetic memories and magnetic switches.

We report a comprehensive study of the physical properties of two series of ${\mathrm{Ti}}_{50-x}{\mathrm{Ni}}_{48+x}{\mathrm{Fe}}_2$ $(x=0.0-2.0)$ alloys synthesized after solution treated and aged at $450{}^{\circ }\mathrm{C}$ using temperature $\left(T\right)$-dependent electrical resistivity $\left(\rho \right)$, Seebeck coefficient $\left(S\right)$, specific heat $\left(C_{\mathrm{p}}\right)$, and thermal conductivity $(\kappa )$ measurements. All measured physical properties indicated that point defects with Ni addition altered martensitic transformation (MT) characteristics from two-stage $B2\leftrightarrow R\leftrightarrow B{19}^{\prime }$ to strain-glass (STG) type in solution-treated alloys, whereas precipitation of ${\mathrm{Ti}}_3{\mathrm{Ni}}_4$ with excess Ni in aged alloys exhibited another $R$-phase transition. These alloys exhibit metallic behavior in $\rho \left(T\right)$ and $S\left(T\right)$; however, their electrical properties vary significantly with increasing $x$, due to the increase in point defects and precipitates. Despite this, solution-treated alloys with $x\ge 1.0$ exhibit a negative temperature coefficient of resistivity below the STG phase due to their continuous formation and growth of $R$ domains. The scattering of charge carriers for both series of alloys in the $B2$ phase appears to be composition independent, although the electronic band structure near Fermi levels varies considerably at each MT. An analysis of $\kappa \left(T\right)$ data reveals that charge carriers contribute more to the MT features than phonons. As Ni content increases, electron-phonon coupling weakens, and phonon modes become harder in these alloys. Furthermore, the entropy change associated with the two intermediate $R$-phase MTs induced by point defects and ${\mathrm{Ti}}_3{\mathrm{Ni}}_4$ precipitates is estimated using $C_{\mathrm{p}}\left(T\right)$, which decreases with lowering transition temperatures and can be explained by theoretical ferroelastic models.

We demonstrate an approach to the structural and electronic property modification of perovskites, focusing on ${\mathrm{Pr}}_2\mathrm{Cu}{\mathrm{O}}_4$, an undoped parent compound of a class of electron-doped copper-oxide superconductors. Currents were passed parallel or perpendicular to the copper oxygen layers with the voltage ramped up until a rapid drop in the resistivity was achieved, a process referred to as “flash.” The current was then further increased tenfold in current-control mode. This state was quenched by immersion into liquid nitrogen. Flash can drive many compounds into different atomic structures with new properties, whereas the quench freezes them into a long-lived state. Single-crystal neutron diffraction of as-grown and modified ${\mathrm{Pr}}_2\mathrm{Cu}{\mathrm{O}}_4$ revealed a $\sqrt{10}\times \sqrt{10}$ superlattice due to oxygen-vacancy order. The diffraction peak intensities of the superlattice of the modified sample were significantly enhanced relative to the pristine sample. Raman-active phonons in the modified sample were considerably sharper. Measurements of electrical resistivity, magnetization, and two-magnon Raman scattering indicate that the modification affected only the Pr-O layers, but not the Cu-O planes. These results point to enhanced oxygen-vacancy order in the modified samples well beyond what can be achieved without passing electrical current. Our work opens a new avenue toward electric field/quench control of structure and properties of layered perovskite oxides.

We demonstrate a thin film ferrimagnet, 48-nm-thick (110)-oriented europium iron garnet, in which the easy plane is perpendicular to the film plane and the hard axis lies in the film plane. We describe the individual contributions to the magnetic anisotropy and the tuning parameters that enable the easy-plane anisotropy landscape to be engineered. The anisotropy landscape is characterized using spin-Hall magnetoresistance measurements. The cubic magnetocrystalline anisotropy, often neglected for iron garnets, is shown to influence the magnetization reversal within the easy plane.