Graphene mediated resistive switching and thermoelectric behavior in lanthanum cobaltate

Abstract

Multifunctional materials are of utmost importance owing to the combination of several functionalities into a single device. We present the multifunctional properties, namely, thermoelectric (TE) for energy harvesting and resistive switching (RS) for memory storage in the LaCoO3 (LCO)–graphene nanocomposite system. The existence of individual phases of LCO and graphene is confirmed from x-ray diffraction and electron microscopy techniques. The x-ray photoelectron spectroscopy measurement reveals the formation of oxygen vacancies in the nanocomposite with the addition of graphene. The bipolar resistive switching behavior observed in a LCO–graphene nanocomposite is explained using space charge limited conduction mechanism and is found to evolve from a trap-limited to a trap-free region with an increase in the graphene volume fraction, which eventually ascribed to the ordering of oxygen vacancies in the nanocomposite system. The endurance plot of the nanocomposite shows a stable RS behavior for consecutive 1000 cycles. On the other hand, the creation of oxygen vacancies in the nanocomposite leads to change in the configurational entropy of charge states of cobalt, which tunes the Seebeck coefficient (α). The decrease in α leads to an increase in the hopping hole concentration (nh) estimated using the classical Heikes formula and is consistent with the increase in the electrical conductivity. The increase in oxygen vacancies leads to point-defect scattering, which further reduces the thermal conductivity of the nanocomposite. The optimized TE parameters show a figure-of-merit of 0.004±0.00048 at 300 K. The simultaneous observation of RS and TE properties in LCO–graphene nanocomposite provides new directions for multifunctional materials.

Synergistic Effect of Work Function and Acoustic Impedance Mismatch for Improved Thermoelectric Performance in GeTe-WC Composite

“…Moreover, the preparation of composite materials is promising for simultaneous optimization of electrical and thermal transport properties to obtain an improved TE performance. This approach allows the utilization of a few transport phenomena that can result in improvement of the σ/κ ratio. − The simultaneous filtering of the charge carrier and enhanced phonon scattering at the interface between the Bi 0.4 Sb 1.6 Te 3 -Cu 2 Se nanocomposite results in an enhanced zT (∼1.6 at 488 K) . Kim et al reported an improved zT (∼1.85) in the PbTe-PbSe composite because of the synergistic effect of reduced κ ph and enhanced α 2 σ .…”

Assessment of Thermoelectric, Mechanical, and Microstructural Reinforcement Properties of Graphene-Mixed Heterostructures

“…TE characteristics of pristine and graphene-reinforced nanocomposites, (a) Seebeck coefficients, (b) electrical conductivities, (c) lattice thermal conductivity (E and H show the total thermal conductivity), and (d) dimensionless figure of merit ( zT ): (A) Bi 0.85 Sb 0.15 -0.5 wt %G ( T = 280 K), (B) Nb-doped SrTiO 3 -RGO ( T = 800 K), (C) Zn 0.98 Al 0.02 O-1.5 wt %RGO ( T = 900 °C), (D) p -phenediamino-modified graphene (PDG) (RT), (E) CoSb 3 /G ( T = 800 K), (F) LaCoO 3 -0.01 wt % G ( T = 300 K), (G) MnTe-GNPs ( T = 823 K), (H) CuInTe 2 /G (80:1) mass ratio ( T = 700 K), (I) SnSe-3.2 wt % MoS 2 /G ( T = 810 K) …”

“…The effect of graphene segregation at the grain interfaces can be evaluated, based on the possible band alignment, depending on the work functions of graphene and the main matrix. As illustrated in Figure 3, the type of contact (Schottky or 16 (C) Zn 0.98 Al 0.02 O-1.5 wt %RGO (T = 900 °C), 17 (D) p-phenediaminomodified graphene (PDG) (RT), 18 (E) CoSb 3 /G (T = 800 K), 19 (F) LaCoO 3 -0.01 wt % G (T = 300 K), 20 (G) MnTe-GNPs (T = 823 K), 21 (H) CuInTe 2 /G (80:1) mass ratio (T = 700 K), 22 (I) SnSe-3.2 wt % MoS 2 /G (T = 810 K). Therefore, these extra boundaries due to smaller grain sizescaused by graphene segregation and grain growth blockingand graphene-matrix interfaces may provide an energy filtering effect for the charge carriers (electrons or holes).…”

Effective thermal conductivity of SrBi4Ti4O15-La0.7Sr0.3MnO3 oxide composite: Role of particle size and interface thermal resistance

“…Based on the available reports in literature, the composite TE materials is an effective strategy to improve the zT via reduction of 𝑘 ph in several systems including SrTiO 3 -graphene [12], LaCoO 3 -graphene [13], CoSb 3 -WO 3 [14], Na 0.77 CoO 2 -Ca 3 Co 4 O 9 [15], (Ca 0.9 Ag 0.1 ) 3 Co 4 O 9 -Ag [16], Ca 3 Co 4 O 9 -La 0.8 Sr 0.2 CoO 3 [17] and also in several other composite systems [18] [19]. However, the studies in the literature on the TE composite materials focus on the improvement of transport properties and rarely consider the effect of 𝑅 𝑖𝑛𝑡 between the phases.…”