[Paper Review] Physical and Dielectric Properties of Polycrystalline LaV$_{0.5}$Nb$_{0.5}$O$_4$

Ashok Kumar, Simranjot K. Sapra+4 more|arXiv (Cornell University)|Jan 22, 2026

Advancements in Solid Oxide Fuel Cells0 citations

TL;DR

The paper analyzes how two sintering temperatures (1000°C and 1250°C) affect the structure, vibrational behavior, electronic states, and dielectric properties of LaV0.5Nb0.5O4 polycrystals.

ABSTRACT

We report a detailed investigation of the structural, electronic, vibrational, and dielectric properties of polycrystalline LaV$_{0.5}$Nb$_{0.5}$O$_4$ samples, prepared at two sintering temperatures (1000\degree C and 1250\degree C). The introduction of Nb$^{5+}$ at the V$^{5+}$ site leads to notable structural and vibrational changes, which can be attributed to their isoelectronic nature and the comparatively larger ionic radius of Nb$^{5+}$. The Rietveld refinement of the X-ray diffraction patterns confirms a coexistence of monoclinic ($P$2$_{1}$/$n$) and scheelite-type tetragonal ($I$4$_{1}$/$a$) phases; for example, with a fraction of 4\% and 96\% for the sample annealed at 1250\degree C. The particle morphology has altered from spherical (1000\degree C) to irregular-shaped (1250\degree C) as a result of increase in annealing temperature. The Raman spectroscopy, Fourier Transform Infrared spectroscopy and X-ray Photoemission Spectroscopy have been used to understand the vibrational and electronic properties. An optical band gap of 2.7~eV for the sample sintered at 1250\degree C is calculated using Ultraviolet-vis diffuse reflectance spectroscopy measurements. The dielectric studies shows the higher dielectric permittivity ($ε$$_{r}$) and lower dielectric loss for the sample annealed at 1250\degree C.

Motivation & Objective

• Investigate how Nb5+ substitution at V5+ site affects structure and vibrational properties of LaVO4-based orthovanadates.
• Characterize phase composition and morphology as a function of sintering temperature.
• Determine electronic structure and oxidation states using XPS and related spectroscopy.
• Evaluate vibrational spectra (Raman, FTIR) and optical band gap via UV-vis DRS.
• Assess dielectric permittivity and loss as a function of temperature and frequency.

Proposed method

• Synthesize LaV0.5Nb0.5O4 via conventional solid-state reaction with calcination at 1000°C and final sintering at 1250°C.
• Perform Rietveld refinement of XRD patterns to quantify monoclinic (P2_1/n) and scheelite-type tetragonal (I4_1/a) phase fractions.
• Use FE-SEM with EDX for morphology and elemental mapping; TEM for microstructure and SAED; HR-TEM for lattice fringes.
• Characterize vibrational properties with Raman and FTIR (ATR) spectroscopy; analyze electronic structure with XPS (Nb, V, La, O core levels).
• Estimate optical band gap from UV-vis diffuse reflectance spectroscopy using Kubelka–Munk transformation and Tauc plot.

Figure 1: The room temperature XRD patterns with Rietveld refinement of (a) LVNO-1000 and (b) LVNO-1250 samples. The open red circles, black solid line, and blue solid line exhibits the experimental, calculated, and the difference between experimental and calculated pattern, respectively. The vertic

Experimental results

Research questions

• RQ1 How does Nb5+ substitution at the V5+ site influence phase stability and the coexisting monoclinic and tetragonal structures in LaVO4-based orthovanadates?
• RQ2 What are the changes in vibrational (Raman/FTIR) and electronic (XPS) signatures due to Nb incorporation and sintering temperature?
• RQ3 How do sintering temperature and resulting phase fractions affect dielectric properties and optical band gap of LaV0.5Nb0.5O4?

Key findings

• XRD shows coexistence of monoclinic P2_1/n and scheelite-type tetragonal I4_1/a phases; LVNO-1000 has ~51% tetragonal and 49% monoclinic, while LVNO-1250 has ~96% tetragonal and 4% monoclinic.
• Morphology changes from spherical particles at 1000°C to irregular shapes and broader grain size distribution at 1250°C, with larger crystallites at higher temperature.
• UV-vis DRS yields optical band gaps of ~3.2 eV (1000°C) and ~2.7 eV (1250°C), indicating band-gap narrowing with increased tetragonal phase content.
• FTIR and Raman spectra confirm VO4^3− presence and Nb incorporation; intensity of certain modes grows with temperature reflecting phase transformation.
• XPS confirms Nb5+, V5+, and La3+ oxidation states; La 3d core-level shows satellite features and slight binding-energy shifts between samples.
• Dielectric studies show higher permittivity and lower dielectric loss for the 1250°C sample, attributed to greater densification and reduced porosity.

Figure 2: The FE-SEM images of the LVNO-1000 sample at (a) 1 $\mu$ m, (b) 500 nm and (c) probed region of scan (at 5 $\mu$ m) with the corresponding elemental mappings of all elements; the FE-SEM images of the LVNO-1250 sample at (d) 1 $\mu$ m, (e) 500 nm and (f) probed region of scan (at 5 $\mu$ m)