Aliovalent Cation Substitution Research Articles

Enhanced room-temperature Na+ ionic conductivity in Na4.92Y0.92Zr0.08Si4O12

Developing cost-effective and reliable solid-state sodium batteries with superior performance is crucial for stationary energy storage. A key component in facilitating their application is a solid-state electrolyte with high conductivity and stability. Herein, we employed aliovalent cation substitution to enhance ionic conductivity while preserving the crystal structure. Optimized substitution of Y3+ with Zr4+ in Na5YSi4O12 introduced Na+ ​ion vacancies, resulting in high bulk and total conductivities of up to 6.5 and 3.3 ​mS ​cm−1, respectively, at room temperature with the composition Na4.92Y0.92Zr0.08Si4O12 (NYZS). NYZS shows exceptional electrochemical stability (up to 10 ​V vs. Na+/Na), favorable interfacial compatibility with Na, and an excellent critical current density of 2.4 ​mA ​cm−2. The enhanced conductivity of Na+ ​ions in NYZS was elucidated using solid-state nuclear magnetic resonance techniques and theoretical simulations, revealing two migration routes facilitated by the synergistic effect of increased Na+ ​ion vacancies and improved chemical environment due to Zr4+ substitution. NYZS extends the list of suitable solid-state electrolytes and enables the facile synthesis of stable, low-cost Na+ ion silicate electrolytes.

Halide solid-state electrolytes for all-solid-state batteries: structural design, synthesis, environmental stability, interface optimization and challenges.

Since the huge breakthrough in 2018, research on halide solid-state electrolytes (SSEs) has set off a new craze. In comparison with oxide and sulfide SSEs, halide SSEs have more balanced properties in various aspects, including ionic conductivity, electrochemical stability window, and moisture resistance. Herein, the overall knowledge and deep understanding of halide SSEs and their practical applications in all-solid-state batteries (ASSBs) are introduced. Firstly, the principle of screening halide SSE components is proposed. Among F, Cl, Br and I anions, the Cl anion is excellent owing to its suitable ionic conductivity and electrochemical stability window. The Sc, Y, and lanthanide elements are also more compatible with Cl anions in terms of electronegativity. Secondly, the structural design theory of halide SSEs with high ionic conductivity and the mechanism of Li ion migration are described. A monoclinic structure is more conducive to Li ion migration, compared with trigonal and orthorhombic structures. Additionally, substitution strategies for halide SSEs are discussed, mainly including dual-halogen, isovalent cation substitution, and aliovalent cation substitution. Furthermore, the mechanism of moisture resistance and synthesis method of halide SSEs are analyzed. Compared with the solid-state reaction and mechanochemistry method, wet chemical synthesis is more likely to achieve scale-up production of halide SSEs. Finally, the application prospects and challenges of halide SSEs in ASSBs are outlined.

Aliovalent Dilute Doping and Nano‐Moiré Fringe Advance the Structural Stability and Thermoelectric Performance in β‐Zn4Sb3 (Adv. Sci. 26/2022)

Thermoelectrics In article number 2201802 by I-Lun Jen, Kuang-Kuo Wang, and Hsin-Jay Wu, aliovalent cation substitution fulfilling by dilute gallium (Ga) ions diminishes the highly-mobile zinc (Zn) ions in zinc antimonide (Zn4Sb3) and optimizes the hole carriers, leading to an ultrahigh thermoelectric power factor. The interstitial metallic Ga elicits formation of nano-moiré fringes, resulting in an ultra-low lattice thermal conductivity. A light-doped Ga-Zn4Sbx crystal performs high thermoelectric performance with superior structural stability by leveraging the ionic and electronic conduction.

Electronic metal-support interaction enhanced ammonia decomposition efficiency of perovskite oxide supported ruthenium

The performance of Ru/La 1-x Sr x AlO 3 catalyst in ammonia decomposition was enhanced by modulating its electronic properties via the strategy of cation substitution. • We present an effective strategy of cation substitution to modulate electronic properties of Ru/La 1-x Sr x AlO 3 catalysts. • Electron-rich Ru facilitates associative desorption of N atoms and accelerates the ammonia decomposition reaction. • Ru/La 0.8 Sr 0.2 AlO 3 catalyst shows high catalytic efficiency and excellent stability during a test perid of 70 h. Ammonia has been considered as a promising hydrogen carrier with high energy storage density and easy transport. Here, we report the ruthenium (Ru) nanoparticles supported on LaAlO 3 , a typical ABO 3 perovskite oxide, as an efficient catalyst for ammonia decomposition. By tailoring the cation substitution of La 3+ by Sr 2+ , the electronic properties of support materials were modulated, which exerts an impact on the electronic state of Ru active sites. It is found that the Ru/La 0.8 Sr 0.2 AlO 3 catalyst has a high hydrogen formation rate and low activation energy. In situ spectroscopic investigation and NH 3 temperature programmed desorption (NH 3 -TPD) analyses indicate the electron-rich state of metallic Ru on the La 0.8 Sr 0.2 AlO 3 support, which promotes associative desorption of N atoms and accelerates NH 3 decomposition reactions. This study provides a universal strategy of aliovalent cation substitution to engineer the electronic properties of metal/oxide catalysts as well as their catalytic activities.

Effect of selected dopants on conductivity and moisture stability of Li3PS4 sulfide solid electrolyte: a first-principles study

The first principle computational screening was performed to investigate the effect of selected dopants for Li3PS4 sulfide solid electrolyte on its ionic conductivity and stability toward moisture. The results suggest that substitution P5+ using isovalent cations whose electronegativity (EN) value is closer to the value of S has more significant effects on the ionic conductivity, whereby W5+ and Sb5+ can improve most. Similarly, aliovalent cation substitutions with compensating changes in the lithium-ion concentration, particularly those with a lower oxidation state and higher EN, such as Cu2+, effectively enhance the lithium-ion conductivity in this structure. For cation dopants, it is found that ionic conductivity improvement of Li3PS4 is the synergetic effect of EN and oxidation number of the dopant as well as the material's lattice parameter change. Oxides of the considered cation dopants can also improve the ionic conductivity of the material but have much lower lithium-ion conductivity than the cases of cation dopants. However, the metal oxide dopants, particularly those derived from soft Lewis' acid cations, show a marginal improvement in moisture stability of the Li3PS4 electrolyte. The effect of halides and metal halide dopants on the lithium-ion conductivity and moisture stability of Li3PS4 electrolyte are also studied. It is found that metal halides are more effective than any other dopants in improving the ionic conductivity of Li3PS4.

Phase Evolution, Electrical Properties, and Conduction Mechanism of Ca12Al14-xGaxO33 (0 ≤ x ≤ 14) Ceramics Synthesized by a Glass Crystallization Method.

Mayenite Ca12Al14O33, as an oxide-ion conductor, has the potential of being applied in many fields, such as solid-oxide fuel cells. However, its relatively low oxide-ion conductivity hinders its wide practical applications and thus needs to be further optimized. Herein, a new recently developed glass crystallization route was used to prepare a series of Ga-doped Ca12Al14-xGaxO33 (0 ≤ x ≤ 14) materials, which is not accessible by the traditional solid-state reaction method. Phase evolution with the content of gallium, the corresponding structures, and their electrical properties were studied in detail. The X-ray diffraction data revealed that a pure mayenite phase can be obtained for 0 ≤ x ≤ 7, whereas when x > 7, the samples crystallize into a melilite-like orthorhombic Ca5Ga6O14-based phase. The electrical conduction studies evidence no apparent enhancement in the total conductivity for compositions 0 ≤ x ≤ 7 with the mayenite phase, and therefore, the rigidity of the framework cations and the width of the windows between cages are not key factors for oxide-ion conductivity in mayenite Ca12Al14O33-based materials, and changing the free oxygen content through aliovalent cation substitution may be the right direction. For compositions with a pure melilite-like orthorhombic phase, the conductivities also mirrored each other and are all slightly higher than those of the mayenite phases. These melilite-like Ca5Ga6O14-based materials show mixed Ca-ion, oxide-ion, and electron conduction. Furthermore, the conduction mechanisms of Ca ions and oxide ions in this composition were studied by a bond-valence-based method. The results suggested that Ca-ion conduction is mainly due to the severely underbonded Ca3 ions and that the oxide ions are most likely transported via oxygen vacancies.

Discovery of a new phosphorviaaliovalent cation substitution: DFT predictions, phase transition and luminescence properties for lighting and anti-counterfeiting applications

Aliovalent substitution induces phase transition, generating new hosts for luminescence applications.

Unexpected aliovalent cation substitution between two NLO materials LiBa3Bi6(SeO3)7F11 and Ba3Bi6.5(SeO3)7F10.5O0.5.

One new combination, alkali-metal and alkaline earth-metal selenite fluoride, LiBa3Bi6(SeO3)7F11 (LBBSF) and its analogue Ba3Bi6.5(SeO3)7F10.5O0.5 (BBSF) were reported here for the first time. Unusual aliovalent cation substitution between them affected the layer thickness and made the bond strains of [SeO3] enhanced, thereby inducing greater distortions and affecting the SHG efficiencies. This work may provide thoughts for exploring new NLO materials.

Implication of aliovalent cation substitution on structural and thermodynamic stability of Gd2Ti2O7: Experimental and theoretical investigations

Multi-cation substituted pyrochlores are potential matrices for immobilization of long-lived high level nuclear waste. In this paper, we report, the structural and thermodynamic stabilities of aliovalent multi cation substituted Gd2Ti2O7 pyrochlore compounds determined by experimental and theoretical methods. A series of cubic pyrochlore-type Gd2-2xCaxZrxTi2O7 (0.0 ≤ x ≤ 0.4) compounds were synthesized and characterized by XRD and Raman spectroscopy techniques. It is observed that incorporation of Ca2+ and Zr4+ at Gd3+ site does not significantly alter crystal lattice of Gd2Ti2O7. Calorimetric studies were carried out to determine the thermodynamic stability of Gd2-2xCaxZrxTi2O7 compounds. The observed data indicate that standard molar enthalpy of formation of Gd2-2xCaxZrxTi2O7 decreases steadily with increasing dopant concentration which has been attributed to increasing distortion of the polyhedra around the cations. These inferences were further supported by DFT calculations.

Anion and cation co-doping of Na4SnS4 as sodium superionic conductors

Na based all-solid-state batteries are one of the most promising candidates for large-scale electrochemical energy storage owing to their low cost and outstanding safety properties. The key enabler of this technology is solid electrolyte with sufficiently high ionic conductivity at room temperature. In this work, the design, synthesis, characterization, and testing of a series of novel fast Na-ion conductors, Na4-x-ySn1-xAxS4-yXy with aliovalent cation (P5+/Sb5+) and anion (Cl−/Br−) substitutions of the parent compound Na4SnS4 are reported. The doped samples crystalize in a new phase with space group I41/acd and show ionic conductivities that are one to four orders of magnitude higher than that of undoped Na4SnS4. R. t. conductivity of 0.64 mS cm−1 is achieved in Na3.7Sn0.8Sb0.2S3.9Cl0.1 with a low activation energy of 0.26 eV. Rietveld refinement against high resolution synchrotron X-ray powder diffraction data reveals that the distribution of the doping ions and the resulted Na vacancies are underlying causes of the enhanced conductivity.

Terahertz-infrared spectroscopy of Ti4+-doped M-type barium hexaferrite

We report on the first detailed investigations of the terahertz-infrared dielectric response of potential multiferroic single crystalline Ti-doped M-type barium hexagonal ferrite, BaFe12-xTixO19, with concentrations of the dopant above (x = 1.15) and below (x = 0.62) the critical concentration that corresponds to changes of the charge compensation mechanism. Employing terahertz time-domain spectroscopy and Fourier-transform infrared spectroscopy, we performed measurements of the spectra of complex dielectric permittivity ε*(ν) = ε′(ν)+iε"(ν) at frequencies ν = 2-8000 cm−1 (0.06–240 THz) and in the temperature interval T = 10–300 K. The effect of aliovalent cation substitution on the low-energy response of barium hexaferrite is analyzed and discussed. A rich set of polarization- and temperature-dependent excitations is observed and their origin assigned to the electronic transition within the ground state 5E of the four-fold coordinated divalent iron, to relaxational dynamics of domains, and to phonon resonances.

Isovalent and aliovalent cation substitutions in the anion sublattice of whitlockite-type ferroelectrics Ca9RE(VO4)7 with RE =Y and Yb

A solid state route was used for the preparation of whitlockite-type solid solutions Ca9Y(NbO4)x(VO4)7–x and Ca9+0.5xYb (GeO4)x(VO4)7–х in both powder and ceramic forms. The complex of methods, including synchrotron powder diffraction, were applied for the characterization of the first-time obtained compounds. The limits of the anionic substitution were found up to х = 0.28 (Nb) and 0.35 (Ge). The synthesized solid solutions show ferroelectric properties. The Curie temperatures Tc were determined and gradually rise with x. The increase of Tc correlates with the enlargement of tetrahedral units upon Nb5+ or Ge4+ substitutions for V5+ cations. The intensity of optical second harmonic generation (SHG) induced by a Nd:YAG laser depends non-monotonically on the grain size in powder Ca9Y(NbO4)x(VO4)7–x samples, marking the length of the phase matching lc = 15 μm for x = 0.28 in comparison with lc = 9.14 μm in Ca9Y(VO4)7. Manifold increase in the SHG intensity in both solid solutions is partly related to the appearance of more polarizable Nb5+ and Ge4+ cations in the E1O4 tetrahedra on the 3-fold axis, resulting in an enlarged birefringence of the materials. The photoluminescence study of the Ca9+0.5xYb(GeO4)x(VO4)7–х reveals the same environment of the Yb3+ ions all alone the solid solution. The intensity of the luminescence rises with germanium substitution for vanadium about 2 times.

Contrasting anion disorder behavior in Sm2Zr2O7 by simultaneous aliovalent cation substitutions and its structural and electrical properties

In the present study, the effect of simultaneous aliovalent cation substitutions on the B site of the pyrochlore type compositions has been studied to understand the anion disorder and its influence on the electrical properties. In this regard, the Sm2Zr2 – x(YNb)x/2O7 (x = 0, 0.25, 0.5, 0.75, 1) compositions were prepared via solid-state reaction route, and the structural and electrical properties of the prepared compositions were analyzed using advanced techniques. The structural analysis studies reveal that the concentration of aliovalent cation substitution has a distinct effect on the structure; the lower concentration of Y and Nb (x ≤ 0.25) destabilizes the system, lowering the distortion, and at higher concentrations (x ≥ 0.5), it stabilizes the system. As a consequence, the distortion of BO6 increases at higher substitutions; thus, the lattice strain of the system increases, manifesting the higher anion disorder in the system. The degree of the anion disorder is further evaluated by the intensity ratio of the Raman intense Eg mode and the T2g mode around 800 cm−1 from the Raman spectrum whose trend is in line with the oxygen x-parameter variation with different concentrations of the aliovalent cation substitution. The electrical properties follow the same trend of the anion disorder and the lattice strain in the system. The maximum conductivity of 4.44 × 10−4 S/cm is obtained for the composition (x = 1) having the maximum anion disorder and lattice strain. The present study demonstrates the interrelationship among the lattice strain, anion disorder, and oxide ion conductivity, which will be helpful in designing and developing new oxide ionic conductors.

Y2(CO3)3·H2O and (NH4)2Ca2Y4(CO3)9·H2O: Partial Aliovalent Cation Substitution Enabling Evolution from Centrosymmetry to Noncentrosymmetry for Nonlinear Optical Response

An effective approach, the partial aliovalent cation substitution (PACS), was successfully employed to develop nonlinear optical (NLO) material. Two novel rare earth carbonates, Y2(CO3)3·H2O (YC) and (NH4)2Ca2Y4(CO3)9·H2O (CYC), were synthesized, which feature the same honeycomb-like framework structure. From YC to CYC, the partial substitution of Y3+ with Ca2+ led to the evolution of space group from centrosymmetric P63/mcm to noncentrosymmetric P63mc. The CYC exhibited a second harmonic generation (SHG) effect of 2.1 × KH2PO4 (KDP) and a deep-UV cutoff edge (<200 nm). It was concluded that the SHG effect originates from the ordered arrangement of (CO3)2– groups and the dipole polarization enhancement of [Ca0.33Y0.67O9] polyhedra. Specifically, the long-range ordered electric field of channels induced the ordered arrangement of (CO3)2– groups. This synthetic approach and SHG-activated induction mechanism may afford new strategies for the design and synthesis of NLO materials.

Studies on order – Disorder transition, lattice expansion and ionic conductivity in aliovalent cation substituted Sm2Zr2O7 System

The effect of simultaneous aliovalent cation substitution on a pyrochlore lattice in (Sm,Zr)2-x(Sc,Ce)xO7 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) was investigated by X-ray diffraction in ambient and high-temperature conditions, electron microscopy, Raman spectroscopy and impedance spectroscopy. The samples were prepared by a conventional high temperature ceramic route. Due to comparable sizes of the ions involved, both the substituent ions diffused randomly into both cation sites leading to an order-to-disorder transition. The lattice thermal expansion coefficient decreases continuously with increased aliovalent cations substitutions which is mainly attributed to the increased diatomic bond energy of the average cation-oxygen bond, unlike the usual trends observed in the systems having phase transition from ordered pyrochlore to disordered fluorite system. The trends in ionic conductivity suggest that it is more governed by the co-operative behaviour of the mobile charge carriers. in the higher substitutions leading to higher activation energies. Hence in the case of pyrochlore type composition, in addition to the lattice disordering, co-operative behaviour of the mobile charge carriers and ionization energy of the individual bond play an important part in determining the electrical behaviour of the system.

Synthesis and photoluminescence control of Ca10.5–1.5xLax(PO4)7:Eu2+ phosphors by aliovalent cation substitution

A range of Ca10.5-1.5xLax(PO4)7:Eu2+phosphors were synthesized by high temperature solid state method. Subsequently we studied the crystal structures and luminescent properties through X-ray diffraction, photoluminescence and photoluminescence excitation, diffuse reflection spectra, Raman spectra and decay curves systematically. Based on the special crystal structure ofβ-Ca3(PO4)2:Eu2+, its emission undergoes a variation from violet–blue to cyan through introducing La3+. The substitution of La3+ for Ca2+ could form some cation vacancies in Ca(4) sites according to the scheme 3Ca2+= 2La3++ □ due to the different ion valence, which compels Eu2+ to migrate from Ca(4) site to other sites. Additionally, the formation of the cation vacancies can further reduce the thermal stability of phosphors.

Influence of aliovalent cation substitutions on the optical properties of In2Cu2O5 system

The influence of aliovalent cation substitutions in In2Cu2O5 system on the optical properties has been investigated through the powder X-ray diffraction coupled with Rietveld analysis, UV–vis–NIR spectroscopy, scanning electron microscope attached with energy dispersive spectrometer. The aliovalent cation substitution affected the optical absorption of the system distinctly as the counter cation substitution of Sc3+ influences the crystal field environment of Cu2+ ions more dominantly than that of the direct substitution of Zn2+ ions. Consequently this allowed the red shift of the absorption edge pronouncedly in the case of Sc3+ substituted samples than that in the Zn2+ substituted ones. The key factor responsible for achieving the larger red shift in Sc3+ substituted sample is due to increased anion polarizability. The assessments of crystal field and tetragonality parameters corroborate the variation of charge transfer energies for the aliovalent cation substitutions. The modified absorption properties translated in enhancing the green chromacity and reflectance of the In2Cu2O5 system even better than the commercially available chromium oxide green (Cr2O3).

A glimpse at topological structures in multiferroic materials

A glimpse at topological structures in multiferroic materials

Optimization of Electronic Domain‐Wall Properties by Aliovalent Cation Substitution

Electronic domain-wall conductance is controlled by chemical aliovalent doping in the p-type semiconductor Er1-xCaxMnO3. Coexisting bound (top panel) and mobile (lower panel) charges at the walls are analyzed using electrostatic force micro­scopy. Emergent doping-related variations are quantified by local transport measurements and explained based on phenomenological theories.

Improving the ionic conductivity of NASICON through aliovalent cation substitution of Na3Zr2Si2PO12

Doping the zirconium site in NASICON (Na3Zr2Si2PO12) with lower valent cations enhanced the ionic transport of the material. Both Na3.2Zr1.8M0.2Si2PO12 (M=Al3+, Fe3+, Y3+) and Na3.4Zr1.8M0.2Si2PO12 (M=Co2+, Ni2+, Zn2+) exhibited a higher bulk conductivity than undoped Na3Zr2Si2PO12 at room temperature. A decrease in the low temperature activation energy for all doped NASICON was observed, which helped contribute to the higher room temperature conductivity. The lower activation energy and enhanced conductivity of doped materials were a result of alterations in the NASICON structure. The charge imbalance created by aliovalent substitution increased the sodium in the lattice resulting in more charge carriers with better mobility. Furthermore, the conductivity was optimized by the ionic radius of the species in the zirconium site. Ultimately, NASICON doped with a +2 oxidation state cation having an ionic radius of approximately 0.73 A (Zn and Co) attained a maximum in conductivity. Zn-doped NASICON displayed the greatest room temperature bulk conductivity of 3.75 × 10−3 S/cm, while Co-doped NASICON demonstrated the greatest total conductivity of 1.55 × 10−3 S/cm.