Structural, magnetic, dielectric, and impedance properties of breathing pyrochlore LiInCr4-xCuxO8 ceramics

The breathing pyrochlore oxide LiInCr 4 O 8 exhibits coupled structural, magnetic, and dielectric functionalities, which motivates interest in multifunctional ceramic applications. Cu-substituted compositions, LiInCr 4- x Cu x O 8 ( x = 0, 0.2, 0.4, 0.5), were synthesized using a solid-state reaction route. In contrast to conventional polycrystalline methods, phase formation was achieved at a lower temperature of 1050°C and within a shorter duration of 24 h. X-ray diffraction confirmed single-phase formation when x ≤0.4 and existence of an impurity phase (In 2 O 3 ) at x = 0.5. Cu incorporation decreases lattice parameters from 8.4125(2) Å to 8.3823(6) Å and increases the breathing factor ( B f ) from 0.1 to 0.1017, attributable to oxygen vacancies and Jahn–Teller distortion. Scanning electron microscopy revealed reduced grain size (∼2 μm) due to lattice strain and suppressed growth. Magnetization measurements showed decreased negative Curie–Weiss temperature and effective magnetic moment. The magnetism indicates a weakened spin gap and emergence of cluster glass behavior, arising from competition between Cr–Cu ferromagnetic interactions and antiferromagnetic order. Detailed studies of dielectric and impedance properties, conducted over a frequency range of 20–3×10 7 Hz and temperature range of 30–350 o C, revealing some interesting behaviors. Dielectric spectroscopy showed an enhanced dielectric constant with frequency-dependent losses: reduced loss at ≤ 5 kHz and increased loss at > 5 kHz, governed by grain boundary contributions at low frequencies, bulk grain effects at high frequencies, and additional oxygen-vacancy-related losses. Impedance increased systematically with Cu substitution up to x = 0.4, followed by a reduction at x = 0.5, reflecting increased grain boundary density and carrier concentration. A low dielectric loss (∼0.01) at high frequencies underscores the potential of Cu-substituted LiInCr 4 O 8 ceramics for microelectronic applications.