Samarium Nickelate Research Articles

‘Fraternal-twin’ ferroelectricity: competing polar states in hydrogen-doped samarium nickelate from first principles

In ferroelectric switching, an applied electric field switches the system between two polar symmetry-equivalent states. In this work, we use first-principles calculations to explore the polar states of hydrogen-doped samarium nickelate (SNO) at a concentration of 1/4 hydrogen per Ni. The inherent tilt pattern of SNO and the presence of the interstitial hydrogen present an insurmountable energy barrier to switch these polar states to their symmetry-equivalent states under inversion. We find a sufficiently low barrier to move the localized electron to a neighboring NiO6 octahedron, a state unrelated by symmetry but equal in energy under a square epitaxial strain (a = b), resulting in a large change in polarization. We term this unconventional ferroelectric a ‘fraternal-twin’ ferroelectric.

Hopping nature of the Hall effect in a samarium nickelate film

We analyzed the temperature dependencies of the DC resistivity and Hall coefficient in thin films of samarium nickelate SmNiO3. A dominating hopping conductivity was revealed in the insulating phase below 400 K, which defines an exponential drop in the Hall coefficient with temperature. The estimated dependencies of the hopping activation energy, Hall mobility, and charge carrier density suggest that small polarons are responsible for hopping. The hopping transport explains the observed sign anomaly of the Hall coefficient in rare-earth nickelates.

Underpinnings behind the magnetic order-to-disorder transition and property anomaly of disproportionated insulating samarium nickelate

Perovskite nickelates (RNiO3), as benchmark materials for exploring underlying physics of phase transitions in strong correlated systems, are well-known for their rich structural characteristics and physicochemical properties. Understanding phase transition from the spin-ordered antiferromagnetic (AFM) state to the spin-disordered paramagnetic (PM) state of RNiO3 requires accurate models at finite temperatures. Here, we investigate the underpinning physics behind the property anomaly and AFM-to-PM transition in samarium nickelate (SmNiO3) using a thermodynamic zentropy approach, which depicts the temperature-dependent total entropy for a system of interest via a nested formula through integration of quantum mechanics and statistical mechanics. The SmNiO3 displays the ground-state of AFM insulator as well as the PM metal and PM insulator at elevated temperatures. It turns out that the magnetic configurational entropy induced by competition among different spatially fluctuating polymorphous spin configurations, contributes to the specific-heat anomaly and the phase transition of SmNiO3 from AFM to PM state. The predicted Néel temperature of 241±25 K for SmNiO3 is in satisfactory agreement with the experimental value. Unlike empirical interpretations in literature, the present work indicates that the magnetic order-to-disorder transition in SmNiO3 is associated with the magnetic configurational entropy due to thermal mixture of multiple spin configurations at elevated temperatures, which can be quantitively captured by the first-principles based thermodynamic zentropy approach.

Valence-Ordered Thin-Film Nickelate with Tri-component Nickel Coordination Prepared by Topochemical Reduction.

The metal-hydride-based "topochemical reduction" process has produced several thermodynamically unstable phases across various transition metal oxide series with unusual crystal structures and nontrivial ground states. Here, by such an oxygen (de-)intercalation method we synthesis a samarium nickelate with ordered nickel valences associated with tri-component coordination configurations. This structure, with a formula of Sm9Ni9O22 as revealed by four-dimensional scanning transmission electron microscopy (4D-STEM), emerges from the intricate planes of {303}pc ordered apical oxygen vacancies. X-ray spectroscopy measurements and ab initio calculations show the coexistence of square planar, pyramidal, and octahedral Ni sites with mono-, bi-, and tri-valences. It leads to an intense orbital polarization, charge-ordering, and a ground state with a strong electron localization marked by the disappearance of ligand-hole configuration at low temperature. This nickelate compound provides another example of previously inaccessible materials enabled by topotactic transformations and presents an interesting platform where mixed Ni valence can give rise to exotic phenomena.

Adaptive thermally tunable radiative cooling with angle insensitivity using phase-change-material-based metasurface

Radiative cooling is the passive cooling of a material with the help of a specific spectral response to emit thermal energy into space through atmospheric transparency windows. However, most of the proposed designs have no dynamically tunable emission response. In this paper, we present a feasible inverse pyramid structure made of a phase change material (PCM) on top of a metallic mirror to realize an adaptive radiative cooler with almost angle-independent emission response. The design uses the thermally controlled PCM called Samarium nickelate (SmNiO3) to actively tune the spectral response of the design, which, in turn, allows the design to radiatively cool itself. The emission response of the design is compatible with atmospheric transmissive windows. As the design heated up to higher temperatures, the peak of the emission spectrum red-shifts and moves toward the atmospheric transparency window.

SmNiO3/SWCNT perovskite composite for hybrid supercapacitor

Modern world has an unparalleled focus on science and technology as an energy storage device as a promising alternative sources to tackle the growing energy crisis and play an important role in economic development. Thus, new approaches and novel promising electrode materials are trying to overcome high energy density without reducing supercapacitors power density and a long lifetime stability. Accordingly, rational flower like structural control of rare earth nickelate-based composite electrodes is also important but very challenging. The role of carbon composites such as single walled carbon nanotube (SWCNT) and multi walled carbon nanotube (MWCNT) with samarium nickelate (SmNiO3) is studied. Herein, the perovskite rare earth SmNiO3, SmNiO3/MWCNT and SmNiO3/SWCNT composites are prepared as potential electrode materials by solvothermal method and never reported before as electrode for supercapacitors. An asymmetric hybrid supercapacitor (SmNiO3/SWCNT//CNT) was fabricated and presented specific capacitance, energy and power density of 170.58 F/g, 53.30 Wh/kg and 749.88 W/kg at 1 A/g. The assembled asymmetric hybrid device exhibited 79.34 % of capacitance retention and 97.52 % of coulombic efficiency even after the continuous 20,000 long cycles. These superior electrochemical properties make the hybrid microflower rare earth nickelate as a good candidate for next generation electrodes in hybrid supercapacitors.

Resistivity modulation of perovskite samarium nickelate with high-valence cations and the underlying mechanism

Perovskite rare earth nickelates possess the electronic phase transition property that can be harnessed for a multitude of exciting applications. Herein, we report the use of high-valence cations (Zn2+ and Al3+) to reconstruct the electronic band structure of samarium nickelate (SmNiO3) and realize reversible resistivity modulation. Under positive gate voltage, the resistivity of SmNiO3 exhibits a colossal increase upon the Zn2+ intercalation and the concurrent electron doping. Under negative gate voltage, the Zn2+ ions are extracted and the resistivity decreases significantly. The resistivity modulation using Zn2+ is non-volatile. Electrochromic behavior is also observed during the Zn2+ insertion and extraction. The electronic phase transition is characterized using various techniques. Moreover, the trivalent Al3+ ions are also investigated as charge carriers to modulate the resistivity of SmNiO3 in a volatile manner. First-principles density functional theory calculations reveal the effect of electron doping on the electronic band structure. The resistivity change of SmNiO3 is mainly attributed to the structural distortion induced by electron doping, rather than the Mott-like insulation. This work demonstrates the feasibility of reversible resistivity modulation of SmNiO3 with the use of high-valence cations under applied voltage, underscoring the potential for applications in novel emerging electronic devices.

Phase-change Fano resonator for active modulation of thermal emission.

Optical modulation of heat emission using spectrally selective infrared (IR) metasurface nanoantenna designs has found potential applications in various fields, including radiative cooling and thermal camouflage. While radiative cooling requires emitters to emit within atmospheric transmissive windows (mainly located at 8-14 μm), thermal camouflage structures have to operate within the non-transmissive window (5-8 μm) to hide an object from thermal imaging systems and cameras. Therefore, a passive nanoantenna structure cannot satisfy both conditions simultaneously. In this paper, we propose an adaptive nanoantenna emitter made of samarium nickelate (SmNiO3) phase change material to cover both functionalities with a single Fano resonator-based design. As the temperature rises, the thermal signature of the nanoantenna at the transmissive window is suppressed; therefore, a better camouflage performance is achieved. The dynamic tunability of switching from radiative cooling to thermal camouflage of the proposed Fano resonator-based design is quantitatively demonstrated using emissive power calculations under different conditions.

Thin-film samarium nickelate as a potential material for methane sensing

Thin-film samarium nickelate as a potential material for methane sensing

Reconfigurable hyperbolic polaritonics with correlated oxide metasurfaces

Polaritons enable subwavelength confinement and highly anisotropic flows of light over a wide spectral range, holding the promise for applications in modern nanophotonic and optoelectronic devices. However, to fully realize their practical application potential, facile methods enabling nanoscale active control of polaritons are needed. Here, we introduce a hybrid polaritonic-oxide heterostructure platform consisting of van der Waals crystals, such as hexagonal boron nitride (hBN) or alpha-phase molybdenum trioxide (α-MoO3), transferred on nanoscale oxygen vacancy patterns on the surface of prototypical correlated perovskite oxide, samarium nickel oxide, SmNiO3 (SNO). Using a combination of scanning probe microscopy and infrared nanoimaging techniques, we demonstrate nanoscale reconfigurability of complex hyperbolic phonon polaritons patterned at the nanoscale with high resolution. Hydrogenation and temperature modulation allow spatially localized conductivity modulation of SNO nanoscale patterns, enabling robust real-time modulation and nanoscale reconfiguration of hyperbolic polaritons. Our work paves the way towards nanoscale programmable metasurface engineering for reconfigurable nanophotonic applications.

Thermochromic SmNiO3-δ thin films deposited by magnetron sputtering and crystallized by soft-annealing in air

Samarium nickelate (SmNiO3) exhibits a metal-insulator transition (MIT) around 120 °C and therefore appears to be an excellent candidate for a new generation of thermochromic solar absorbers. Nevertheless, this kind of perovskite is classically obtained under extreme conditions to stabilize the metastable Ni3+ oxidation state. Here, we show that SmNiO3-δ thin films can be synthesized under soft-annealing as the habitual orthorhombic distorted perovskite structure. The layers were deposited by reactive magnetron co-sputtering and subsequently annealed for crystallization for 2 h at 500 °C in air. Structural characterization was carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques, while optical and electrical properties were determined by Fourier transform infrared spectroscopy (FTIR) and the four-point probe method, respectively. The Ni3+ ion was confirmed by Electron energy loss spectroscopy (EELS). Finally, reversible thermochromic behavior was observed with an MIT temperature estimated at 138 °C and an IR contrast of 19%.

Influence of defects on antidoping behavior in SmNiO3

Samarium nickelate ($\mathrm{Sm}\mathrm{Ni}{\mathrm{O}}_{3}$) is a representative quantum material, presenting ``exotic'' properties including strong correlations and metal-to-insulator transition. It was also shown that $\mathrm{Sm}\mathrm{Ni}{\mathrm{O}}_{3}$ presents the unusual antidoping effect, where the resistivity of the material increases with doping instead of decreasing. In this paper, we study intrinsic defects in this compound, and discuss the antidoping behavior in the presence of these defects. Our results show that the negatively charged oxygen vacancy (${V}_{\text{O}}^{\ensuremath{-}2}$) can be very stable, and the extra electrons move towards the small octahedra (${\mathrm{Ni}}^{4+}$ sites), similar to the antidoping effect in the pristine material. This indicates that antidoping should still be observed even in the presence of defects.

A first-principles study of the proton and oxygen migration behavior in the rare-earth perovskite SmNiO3

Transition-metal oxide perovskites usually exhibit mixed ionic and electronic conductivity and have been widely investigated as electrode materials for use in solid-oxide fuel cells. Recently, samarium nickelate SmNiO3 was found experimentally to show promising potential for use in proton-conducting fuel cells. To understand the ionic conductivity of SmNiO3, the oxygen and proton diffusion therein are investigated via density functional theory calculations in this work. Based on the vacancy hopping mechanism, oxygen diffusion in SmNiO3 shows a migration barrier of 0.84 eV. The proton diffusion is studied in terms of different diffusion mechanisms, including reorientation, intraoctahedral, and interoctahedral hopping. The migration barrier for intraoctahedral migration is calculated to be lower than that for interoctahedral hopping. To realize long-range diffusion, the proton is predicted to exhibit reorientation and intraoctahedral hopping. These findings provide a theoretical guide for the development of mixed ionic and electronic perovskite conductors.

Temperature-independent thermal radiation

Thermal emission is the process by which all objects at nonzero temperatures emit light and is well described by the Planck, Kirchhoff, and Stefan-Boltzmann laws. For most solids, the thermally emitted power increases monotonically with temperature in a one-to-one relationship that enables applications such as infrared imaging and noncontact thermometry. Here, we demonstrated ultrathin thermal emitters that violate this one-to-one relationship via the use of samarium nickel oxide (SmNiO3), a strongly correlated quantum material that undergoes a fully reversible, temperature-driven solid-state phase transition. The smooth and hysteresis-free nature of this unique insulator-to-metal phase transition enabled us to engineer the temperature dependence of emissivity to precisely cancel out the intrinsic blackbody profile described by the Stefan-Boltzmann law, for both heating and cooling. Our design results in temperature-independent thermally emitted power within the long-wave atmospheric transparency window (wavelengths of 8 to 14 µm), across a broad temperature range of ∼30 °C, centered around ∼120 °C. The ability to decouple temperature and thermal emission opens a gateway for controlling the visibility of objects to infrared cameras and, more broadly, opportunities for quantum materials in controlling heat transfer.

High-density electron doping of SmNiO3 from first principles

Recent experimental work has realized a new insulating state of samarium nickelate (SmNiO$_3$), accessible in a reversible manner via high-density electron doping. To elucidate this behavior, we use the first-principles density functional theory (DFT) + U method to study the effect of added electrons on the crystal and electronic structure of SmNiO$_3$. First, we track the changes in the crystal and electronic structure with added electrons compensated by a uniform positive background charge at concentrations of $\frac{1}{4}$, $\frac{1}{2}$, $\frac{3}{4}$, and 1 electrons per Ni. The change in electron concentration does not rigidly shift the Fermi energy; rather, the added electrons localize on NiO$_6$ octahedra causing an on-site Mott transition and a change in the density of states resulting in a large gap between the occupied and unoccupied Ni $e_g$ orbitals at full doping. This evolution of the density of states is essentially unchanged when the added electrons are introduced by doping with interstitial H or Li ions.

Electrical conductivity and infrared ray photoconductivity for lattice distorted SmNiO<sub>3</sub> perovskite oxide film

The metal-to-insulator transitions achieved in rare-earth nickelate (<i>R</i>NiO<sub>3</sub>) receive considerable attentions owning to their potential applications in areas such as temperature sensors, non-volatile memory devices, electronic switches, etc. In contrast to conventional semiconductors, the <i>R</i>NiO<sub>3</sub> is a typical electron correlation system, in which the electronic band structure is dominant by the Coulomb energy relating to the <i>d</i>-band and its hybridized orbitals. It was previously pointed out that lattice distortion can largely influence the electronic band structures and further significantly affect the electronic transportation properties, such as the resistivity and metal-to-insulator transition properties. Apart from directly measuring the transportation performance, the variations in the origin of carrier conduction and orbital transitions relating to the strain distortion of <i>R</i>NiO<sub>3</sub> can also be reflected via their optical properties. In this work, we investigate the optical properties of samarium nickel (SmNiO<sub>3</sub>) thin films when lattice distortions are induced by interfacial strains. To introduce the interfacial strain, the SmNiO<sub>3</sub> thin films are epitaxially grown on the strontium titanate (SrTiO<sub>3</sub>) and lanthanum aluminate (LaAlO<sub>3</sub>) single crystal substrates by using the pulsed laser deposition. A bi-axial tensile distortion happens when the SmNiO<sub>3</sub> thin films are grown on SrTiO<sub>3</sub> due to the smaller lattice constant of SmNiO<sub>3</sub> than that of SrTiO<sub>3</sub>, while the one grown on LaAlO<sub>3</sub> is strain-relaxed. We measure the infrared radiation (IR) transmission spectra of the SmNiO<sub>3</sub> thin films grown on various substrates. The obtained IR transmission spectra are fitted by a Drude-Lorentz model and further converted into the curves of photoconductivity versus IR frequency. Comparing the difference in photoconductance between low frequency and high frequency reflects the two different origins of the conduction, which are related to intraband transition and band-to-band transition, respectively. The smaller photoconductance is observed for SmNiO<sub>3</sub>/SrTiO<sub>3</sub> than for SmNiO<sub>3</sub>/LaAlO<sub>3</sub> at low frequency, and this is expected to be caused by the suppression of free carriers as reported previously for tensile distorted SmNiO<sub>3</sub>. The consistence is obtained when further measuring the electronic transportation such as temperature-dependent electrical resistivity, as a higher resistivity is observed for SmNiO<sub>3</sub>/SrTiO<sub>3</sub> than for SmNiO<sub>3</sub>/LaAlO<sub>3</sub>. The combination of the investigation of electrical transport with that of infrared transmission indicates that the tensile distortion in structure stabilizes the insulating phase to eliminate a pronounced metal-to-insulator transition and elevates the transition temperature. This is related to the respective twisting of the NiO<sub>6</sub> octahedron when tensile distortion regulates the valance state of the transition metal and further opens the band gap, which is further confirmed by results of the X-ray absorption spectrum.

Ultrafast photoinduced insulator-metal transition in epitaxial samarium nickelate thin films investigated by time-resolved terahertz spectroscopy

We investigate the ultrafast dynamic behavior of photoinduced insulator-metal phase transition in an epitaxially grown $\mathrm{SmNi}{\mathrm{O}}_{3}$ thin film by using time-resolved terahertz (THz) spectroscopy at different excitation fluences. It is found that the relaxation of the photoexcited carriers is characterized by two components with different time scales: (i) an ultrafast one with time constant varying between 0.3 ps (at 4.4 $\mathrm{mJ}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$) and 0.35 ps (at 0.88 $\mathrm{mJ}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$) and (ii) a slow one with a time constant varying between 1.7 ps (at 2 $\mathrm{mJ}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$) and 4.7 ps (at 0.88 $\mathrm{mJ}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$). These relaxation times could be primarily attributed to the coexistence of conducting and insulating charge-ordering domains. The observed behavior of the transient THz conductivity of $\mathrm{SmNi}{\mathrm{O}}_{3}$ thin film is well fitted by the Drude-Smith model, revealing that insulating domains emerge between the metallic domains, which in turn increase the carrier confinement during the relaxation process. Furthermore, the ultrafast dynamic behavior at different temperatures suggests that the insulating gap shrinks gradually between the Ni $3d$ and O $2p$ states as the temperature applied to the film increases. Our experimental findings pave the way to scientific opportunities and to technological applications of epitaxially grown $\mathrm{SmNi}{\mathrm{O}}_{3}$ thin film such as ultrafast optical switching and modulation devices.

Deposition of Transition Temperature Controlled Thermochromic NdxSm1-xNiO3 Films by Spin Coating

The precursor samarium nickelate or samarium-neodimium nickelate films were fabricated by a spin coating method using Sm-Ni or Nd-Sm-Ni aqueous solutions, and SmNiO3 and Nd0.5Sm0.5NiO3 films were obtained by heat-treatment of the precursor films at 750 °C in oxygen atmosphere. The resulting SmNiO3 and Nd0.5Sm0.5NiO3 films showed an electrical transition with the transition temperatures of 124.0 and 32.5 °C, respectively. Both of the films showed optical thermochromic properties at the above mentioned transition temperatures.

Metal-Insulator Transition of strained SmNiO3 Thin Films: Structural, Electrical and Optical Properties

Samarium nickelate (SmNiO3) thin films were successfully synthesized on LaAlO3 and SrTiO3 substrates using pulsed-laser deposition. The Mott metal-insulator (MI) transition of the thin films is sensitive to epitaxial strain and strain relaxation. Once the strain changes from compressive to tensile, the transition temperature of the SmNiO3 samples shifts to slightly higher values. The optical conductivity reveals the strong dependence of the Drude spectral weight on the strain relaxation. Actually, compressive strain broadens the bandwidth. In contrast, tensile strain causes the effective number of free carriers to reduce which is consistent with the d-band narrowing.

A study on the kinetics of syngas production from glycerol over alumina-supported samarium–nickel catalyst

The current paper reports on the kinetics of syngas production from glycerol pyrolysis over the alumina-supported nickel catalyst that was promoted with samarium, a rare earth element. The catalysts were synthesized via wet-impregnation method and its physicochemical properties were subsequently characterized. Reaction studies were performed in a 10 mm-ID stainless steel fixed bed reactor with reaction temperatures maintained at 973, 1023 and 1073 K, respectively, employing weight-hourly-space-velocity of 4.5 × 104 ml g−1 h−1. The textural property examination showed that BET specific surface area was 2.09 m2 g−1 for the unpromoted catalyst while the samarium promoted catalyst has 2.68 m2 g−1. Interestingly, the results were supported by the FESEM images which showed that the promoted catalyst has smaller particle size compared to the unpromoted catalyst. Furthermore, the NH3- and CO2-TPD analyses proved that the strong and weak acid-basic sites were present. During glycerol pyrolysis, the syngas was produced directly from the glycerol decomposition. This has created H2:CO ratios that were always lower than 2.0, which is suitable for Fischer-Tropsch synthesis. The activation energy based on power law modeling for the unpromoted catalyst was 35.8 kJ mol−1 and 23.4 kJ mol−1 for Sm-promoted catalyst with reaction order 1.20 and 1.10, respectively. Experimental data were also fitted to the Langmuir–Hinshelwood model. Upon subjected to both statistical and thermodynamics consistency criteria, it can be conclusively proved that single-site mechanisms with associative adsorption of glycerol best describe the glycerol pyrolysis over both unpromoted and Sm promoted catalyst in the current work, with regression coefficient values of more than 0.9.