Unlocking the Sensing Potential of Mn_1.5Cr_1.5O₄ Spinel Nanocomposite by Exploring Humidity-Dependent Dielectric Characteristics

This study explores the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {Mn}_{{1}.{5}}\text {Cr}_{{1}.{5}}\text {O}_{{4}}$ </tex-math></inline-formula> nanocomposite, a promising spinel oxide, for high-performance humidity sensing via its dielectric properties. The nanocomposite was synthesized using the solution combustion method, enabling precise control over grain size and porosity to enhance its hydrophilic characteristics. Structural and morphological analyses via X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the formation of a single-phase spinel structure with well-defined porosity and grain boundaries (GBs). The fabricated sensor exhibited a remarkable dielectric response, with the dielectric constant increasing 472 times at 95% relative humidity (RH) compared to 11% RH at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathbf {{10}^{{2}}}$ </tex-math></inline-formula> Hz. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {Mn}_{{1}.{5}}\text {Cr}_{{1}.{5}}\text {O}_{{4}}$ </tex-math></inline-formula> sensor demonstrated outstanding performance, including low hysteresis (1.92% RH), excellent stability, superior linearity (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2} =0.9834$ </tex-math></inline-formula>), and rapid response (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim {11}\textbf {. {5}}$ </tex-math></inline-formula> s) and recovery (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim {15} $ </tex-math></inline-formula> s) times, surpassing conventional humidity sensors. The sensing mechanism was systematically analyzed through variations in the dielectric constant, normalized loss tangent, complex modulus, and alternating current (ac) conductivity, revealing that the conduction process is governed by electron and ion transport, along with dipole interactions across the entire RH range. These results establish <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {Mn}_{{1}.{5}}\text {Cr}_{{1}.{5}}\text {O}_{{4}}$ </tex-math></inline-formula> nanocomposite as a highly promising material for next-generation humidity sensors, offering superior sensitivity, reliability, and rapid response for advanced sensing applications.