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. 2025 Aug 21;15(36):29703-29719.
doi: 10.1039/d5ra04138d. eCollection 2025 Aug 18.

Implementing a solid-state synthesis route to tune the functional properties of NaCdP3O9 metaphosphate: optical characteristics, ionic conductivity, and dielectric behavior

M Karray  1 , I Garoui  1 , M Akermi  2 , R Djebali  3 , A Oueslati  1 , M Gargouri  1
Affiliations

Implementing a solid-state synthesis route to tune the functional properties of NaCdP3O9 metaphosphate: optical characteristics, ionic conductivity, and dielectric behavior

M Karray et al. RSC Adv. .

Abstract

An in-depth analysis of NaCdP3O9 was performed, exploring its structural framework, vibrational dynamics, optical absorption, and electrical behavior. The compound was synthesized using a low-cost, conventional solid-state route, resulting in a well-defined orthorhombic crystal structure assigned to the P212121 space group. Optical studies identified a direct energy band gap of 3.88 eV. Dielectric measurements revealed pronounced dependencies on both frequency and temperature, with high dielectric permittivity values at low frequencies (ε' ≈ 1.19 × 103). Charge transport is primarily facilitated through a polaron hopping mechanism. DC conductivity followed Arrhenius behavior, indicating thermally activated motion of sodium ions with an activation energy of 0.45 eV. Additionally, AC conductivity and dielectric analyses support a conduction process involving localized charge carriers surmounting correlated energy barriers, in agreement with the correlated barrier hopping (CBH) model. This study underscores the synergy between solid-state synthetic strategies and functional property optimization, positioning metaphosphate materials as strong candidates for future sustainable electronic technologies.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1. The synthesis steps for NaCdP3O9via the solid-state method.
Fig. 2
Fig. 2. (a) X-ray diffraction (XRD) of NaCdP3O9 at room temperature. (b) The Debye–Scherrer plot for NaCdP3O9 compound.
Fig. 3
Fig. 3. Infrared spectrum analysis of NaCdP3O9 at room temperature.
Fig. 4
Fig. 4. (a) The UV-vis absorbance spectrum and dA/dλ as a function of λ (inset) for the phosphors NaCdP3O9. (b) Variation of (αhυ)2 and (αhυ)1/2 plots vs. hυ for band gap of NaCdP3O9 and variation of ln(αhυ) against ln(hυ − Eg) determination (inset). (c) Determining the Urbach energy.
Fig. 5
Fig. 5. Nyquist plot of NaCdP3O9 compound, at different temperatures with equivalent circuit model in the inset.
Fig. 6
Fig. 6. (a) Variation of real part of the impedance with angular frequency at various temperatures for NaCdP3O9. (b) Variation of imaginary part of the impedance with angular frequency at various temperatures for NaCdP3O9.
Fig. 7
Fig. 7. (a) Frequency-dependent variation of the electrical conductivity of NaCdP3O9 at different temperatures. (b) Evolution of ln(σdc × T) versus the reciprocal of temperature and the deduced activation energy value. (c) The temperature dependence of the frequency exponent “s”.
Fig. 8
Fig. 8. Sodium-ion diffusion pathway in the NaCdP3O9 structure along the [111̄] direction.
Fig. 9
Fig. 9. (a) Evolution of the real part of the permittivity as a function of the angular frequency of the NaCdP3O9 at various temperatures. (b) Evolution of the imaginary part of the permittivity as a function of the angular frequency of the NaCdP3O9 at various temperatures.
Fig. 10
Fig. 10. The temperature dependence of the frequency exponent “m”.
Fig. 11
Fig. 11. (a and b) Evolution of the imaginary part of the permittivity as a function of the angular frequency of the NaCdP3O9 at various temperatures.
Fig. 12
Fig. 12. Evolution of ln(ωp × T) versus the reciprocal of temperature.
Fig. 13
Fig. 13. Combined Z′′ and M′′ spectroscopic plots.
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