Nb Substitution For Zr Research Articles

Weyl-like points from band inversions of spin-polarised surface states in NbGeSb

Band inversions are key to stabilising a variety of novel electronic states in solids, from topological surface states to the formation of symmetry-protected three-dimensional Dirac and Weyl points and nodal-line semimetals. Here, we create a band inversion not of bulk states, but rather between manifolds of surface states. We realise this by aliovalent substitution of Nb for Zr and Sb for S in the ZrSiS family of nonsymmorphic semimetals. Using angle-resolved photoemission and density-functional theory, we show how two pairs of surface states, known from ZrSiS, are driven to intersect each other near the Fermi level in NbGeSb, and to develop pronounced spin splittings. We demonstrate how mirror symmetry leads to protected crossing points in the resulting spin-orbital entangled surface band structure, thereby stabilising surface state analogues of three-dimensional Weyl points. More generally, our observations suggest new opportunities for engineering topologically and symmetry-protected states via band inversions of surface states.

Molecular dynamics simulations with machine learning potential for Nb-doped lithium garnet-type oxide Li7−xLa3(Zr2−xNbx)O12

Lithium garnet-type oxide ${\mathrm{Li}}_{7}{\mathrm{La}}_{3}{\mathrm{Zr}}_{2}{\mathrm{O}}_{12}$ (LLZO) is one of the most promising solid electrolyte materials. In this study, the Li conduction properties of Nb-doped LLZO, ${\mathrm{Li}}_{6.75}{\mathrm{La}}_{3}({\mathrm{Zr}}_{1.75}{\mathrm{Nb}}_{0.25}){\mathrm{O}}_{12}$, have been investigated by molecular dynamics simulations with the machine learning potential. It is shown that Nb-doped LLZO holds a high-conductivity cubic structure at low temperatures. Two kinds of Li occupation sites, $24d$ and $96h$, are correctly predicted, which form the three-dimensional network of the Li migration pathway. The Li conductivity at 298 K and the activation energy are obtained as ${\ensuremath{\sigma}}_{\mathrm{Li}}=5.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{3.33333pt}{0ex}}\mathrm{S}/\mathrm{cm}$ and ${E}_{a}=223\phantom{\rule{3.33333pt}{0ex}}\mathrm{meV}$, respectively, which are in reasonably good agreement with the experimental data. The free energy difference between the $24d$ and $96h$ sites is expected to be negligibly small. This most likely contributes a high Li conductivity in the Nb-doped LLZO. The Nb substitution for Zr is accompanied with the Li vacancy formation due to the charge neutrality condition, which stabilizes the cubic phase and enhance the Li conduction. The Nb substitution, however, also has a negative effect. The supervalency of the ${\mathrm{Nb}}^{5+}$ ion destabilizes the Li atoms at the surrounding $96h$ sites. The Li conductivity in Nb-doped LLZO is determined by trading off between these effects.

Rational Design of a LiNbO3-like Nonlinear Optical Crystal, Li2ZrTeO6, with High Laser-Damage Threshold and Wide Mid-IR Transparency Window.

With existing and emerging technologies urgently demanding the expansion of the laser wavelengths, high-performance nonlinear optical (NLO) crystals are becoming indispensable. Here, a prospective NLO crystal, Li2ZrTeO6, is rationally designed by the element substitution of Nb for Zr and Te from LiNbO3, which has been recognized as one of the most commercial NLO crystals. Li2ZrTeO6 with R3 symmetry inherits the structural merits of LiNbO3 (space group R3 c) and thus meets the requirements for NLO applications, including noncentrosymmetric crystal structure, moderate birefringence, and phase-matchability. Moreover, it can be exploited to achieve more outstanding optical damage resistant behavior (>1.3 GW cm-2), exceeding 22 times that of LiNbO3, which is more suitable for high-energy laser applications. Notably, this compound displays the widest IR absorption edge (7.4 μm) among all of the noncentrosymmetric tellurates reported so far. These excellent attributes suggest that Li2ZrTeO6 is a promising candidate for providing high NLO performance. The substitution of Nb for Zr and Te from LiNbO3 demonstrates a viable strategy toward the rational design of NLO crystals with anticipated properties.

A Centimeter-Size High Toughness Zr-Cu-Al-Nb Bulk Metallic Glass with Nano-Crystallization and Phase Separation

In this paper, a centimeter-size Zr-Cu-Al-Nb bulk metallic glass (BMG) with high notch toughness of 107±13 MPa∙m0.5 was designed and fabricated by copper mold casting. With 1% Nb substitution for Zr in Zr48Cu45Al7 glass forming alloy, the glass forming ability (GFA) and toughness of the BMG were enhanced significantly. The coexistence of nano-crystallization and phase separation in the glassy matrix was observed in Zr47Cu45Al7Nb1, which would possibly lead to the high toughness of this alloy due to the easy and populous nucleation of shear bands and the increasing resistance of shear band propagation. The influences of nano-crystallization and phase separation on the toughness of BMGs are discussed in detail. The strategy utilized in this study provides a novel approach in search for new BMGs with high toughness and good GFA.

Effects of Nb substitution for Zr on the phases, microstructure and magnetic properties of Co80Zr18−xNbxB2 melt-spun ribbons

The phases, microstructure, and magnetic properties of Co80Zr18−xNbxB2 (x=1, 2, 3, and 4) melt-spun ribbons were investigated. The small substitution of Nb for Zr in the Co–Zr–B melt-spun ribbons resulted in the improvement of magnetic properties, especially the coercivity. The main effect of added Nb on the coercovity of Co–Zr–Nb–B melt-spun ribbons, originated from modification of the grain size of Co11Zr2 phase. The coercivity of the Co–Zr–Nb–B melt-spun ribbons depends on the annealing temperature. The optimal magnetic properties of Hc=5.1kOe, and (BH)max=3.4MGOe were obtained in the Co80Zr15Nb3B2 melt-spun ribbons annealed at 600°C for 3min.

Tunable dielectric properties of lead barium zirconate niobate films

The effect of substitution of niobium for zirconium on tunable behavior of lead barium zirconate (PBZ) films was investigated. Lead barium zirconate niobate films were grown on Pt∕Ti∕SiO2∕Si substrates using chemical solution deposition method. The substitution of Nb for Zr enhances tunable properties of PBZ films. The dielectric tunabilities are excellent, all higher than 45% with a maximum=60%. The substitution of Nb for Zr raises values of figure of merit (FOM) of films. The maximum FOM takes place at 5mol% Nb with a value of 90, which is about three times that of the corresponding PBZ film.

Local structure of Al-and Fe-based metallic glasses

The local atomic structures of Fe-and Al-based amorphous metallic glasseshave been investigated by the pair density function (PDF) analysis ofneutron diffraction data. In the Fe system, chemical substitution at thetransition metal ion sites induces significant changes of the local structuralenvironment. With the substitution of Nb for Zr and Mn for Fe, a pre-peak in thestructure function is observed that is indicative of short-range chemicalrearrangement. This is accompanied by a reduction of volume in realspace and a contraction of interatomic pair correlations that could inturn be associated with stronger glass forming ability. In the Al–Ni–Ndsystem, using the isotope difference neutron PDF technique, the localenvironments for Ni and Nd were separately determined. The Ni ions tendto form strong interactions with Al with significant shortening of thebond length and weaker interactions with Nd. The local Ni–Al cluster isalmost spherical with a coordination close to twelve nearest neighbours,while Ni–Ni chemical short-range ordering is quite strong as indicated bythe change of amplitude of the pre-peak with the isotopic substitution.On the other hand, the local Nd environment is more disordered withtwo separate Nd–Al coordination environments and weaker clustering.