Electrical Resistance Behavior and Cycle-to-Cycle Repeatability in Natural Graphite Flake-Based Devices

This work investigates the potential of natural flake graphite─extracted from graphite-bearing saprolite from the Jequitinhonha Complex (Brazil)─as a structurally well-ordered, low-cost alternative for tunable electronic devices. Four distinct samples were produced from these flakes and deposited via drop-casting of the dispersion into the coupling region between two microstrip transmission lines. Systematic DC electrical characterization was performed across successive measurement cycles and dynamic resistance-switching tests, and the results were compared with previously reported reduced graphene oxide (rGO) systems. All samples exhibited a controllable and nonohmic decrease in electrical resistance with increasing applied current, satisfying an important preliminary electrical requirement for future radio frequency (RF) and microwave tunable device applications. Although the first measurement cycle exhibits distinct behavior, the electrical response stabilizes and shows stable cycle-to-cycle repeatability from the third cycle onward. Despite the limited precise control over film formation inherent to the technique employed, the results were reasonably consistent with the nominal amount of deposited material. Although the present measurements do not allow these contributions to be quantitatively decoupled, the observed results align with two underlying mechanisms: Joule heating-related thermal effects and reconfiguration of the conductive percolation network. Importantly, time-dependent measurements indicate that, compared to rGO-based systems, devices based on natural flake graphite exhibit a negligible memory effect, showing only a slight fluctuation while undergoing a near-complete recovery of their baseline resistance. These results are important because they provide, for the first time, an assessment of natural flake graphite for such applications. Moreover, they highlight the fundamental role of granular structure in the electrical conductivity of graphitic systems and position this class of materials as promising and cost-effective candidates for next-generation tunable electronic applications.