Tunability of structure from ordered to disordered and its impact on ionic conductivity behavior in the Nd2−yHoyZr2O7 (0.0 ≤ y ≤ 2.0) system

Abstract

The present paper describes a detailed investigation of the nature of the order-disorder transition in the Nd 22y Ho y Zr 2 O 7 system, over the entire composition range (0.0 ¡ y ¡ 2.0), using a combination of diffraction and spectroscopic analysis techniques. The complete series of solid solutions has been prepared by the gel combustion technique followed by high temperature sintering. Detailed structural characterization of the prepared samples using X-ray diffraction studies confirmed their single-phase solid solution formation throughout the series, as well as identifying the transformation of the system from an ordered pyrochlore structure (0.0 ¡ y ¡ 0.8) to a disordered fluorite-type structure (0.8 , y ¡ 2.0). Micro-Raman studies further supported the structural information. Micro-structural studies by SEM revealed dense products with uniform grain distribution in these materials. Comprehensive studies were performed to investigate the ionic conductivity behavior of these solid solutions in correlation with the structural transformations using AC impedance spectroscopy. A detailed analysis of ionic conductivity and related parameters, such as activation energies, etc. corresponding to individual conduction mechanisms such as bulk and grain boundary conduction, clearly correlated the effect of structural transformation on these charge transport properties. The composition Nd 1.2 Ho 0.8 Zr 2 O 7 with the pyrochlore structure has been found to show the highest ionic conductivity in the entire series, which has been attributed to a combined effect of increasing carrier concentration and their preferred movement through an ordered array of vacant anion sites.

Structural study of holmium zirconate nanoparticles obtained through carbon neutral sol-gel process

“…The value of goodness of fit (GOF) is close to 5% as seen in Table 2. ion-exchange based sol-gel method in this study is in excellent agreement with the data obtained through Polymerized-Complex Method (PCM) [19] and gel combustion technique followed by high temperature sintering [21] . 5 shows the comparison between the XRD patterns of holmium hafnate (Ho2Hf2O7) [22] and holmium zirconate (Ho2Zr2O7) synthesised through alginate based sol gel method.…”

Molecular Dynamics Study of Complex Dopant Electrolyte Nd2–xHoxZr2O7: Structure, Conductivity, and Thermal Expansion

“…As mentioned before, ionic conductivity is calculated from Nernst-Einstein equation that is based on MSD. It was noticeable that ionic conductivity maximum occurred at x = 0.6, which was confirmed by experimental results for bulk ionic conductivity [31]. Moreover, this figure indicates that complex dopant SZ (like NdHoSZ) at adequate ratio (x = 0.6) had higher ionic conductivity than NdSZ (x = 0.0) and HoSZ (x = 2.0).…”

“…Besides, temperature dependence of ionic conductivity at different compositions of Nd and Ho provided accurate results by MD simulation and least square method to the experimental bulk ionic conductivity [31]. Since the results of simulations and experimental data were in good agreement with each other, the simulations are acceptable (see Figs.…”

Induced oxygen vacancies and their effect on the structural and electrical properties of a fluorite-type CaZrO3–Gd2Zr2O7 system

“…The introduction of larger Ca ions in place of Gd ions is expected to expand the lattice in accordance with Vegard's law 24 which is a commonly observed trend in many similar substitutions. [25][26][27] In the present system, the decrease in the fundamental lattice vector of the system can be attributed to the Coulomb considerations when a trivalent cation is substituted by a divalent one. The condition of charge neutrality would require a few oxygen ions to be removed, in effect introducing anion vacancies in the lattice that would in turn lead to a lattice contraction.…”