Graphene/Strontium Titanate: Approaching Single Crystal–Like Charge Transport in Polycrystalline Oxide Perovskite Nanocomposites through Grain Boundary Engineering

Abstract

Grain boundaries critically limit the electronic performance of oxide perovskites. These interfaces lower the carrier mobilities of polycrystalline materials by several orders of magnitude compared to single crystals. Despite extensive effort, improving the mobility of polycrystalline materials (to meet the performance of single crystals) is still a severe challenge. In this work, the grain boundary effect is eliminated in perovskite strontium titanate (STO) by incorporating graphene into the polycrystalline microstructure. An effective mass model provides strong evidence that polycrystalline graphene/strontium titanate (G/STO) nanocomposites approach single crystal‐like charge transport. This phenomenological model reduces the complexity of analyzing charge transport properties so that a quantitative comparison can be made between the nanocomposites and STO single crystals. In other related works, graphene composites also optimize the thermal transport properties of thermoelectric materials. Therefore, decorating grain boundaries with graphene appears to be a robust strategy to achieve “phonon glass–electron crystal” behavior in oxide perovskites.

Modulation of Charge Transport at Grain Boundaries in SrTiO3: Toward a High Thermoelectric Power Factor at Room Temperature

“…We further computed the weighted mobility (μ w ) of the LSTO samples from the measured electrical conductivity and Seebeck coefficients using the approach reported recently by Snyder et al 7 , 45 In detail, the LSTO ceramic was treated as a homogeneous phase with acoustic phonon scattering as the dominating scattering mechanism (transport parameter s = 1), the reduced Fermi energy level η at each temperature was extracted from the Seebeck coefficients using eq 4 , and then, the temperature-dependent transport coefficient σ E 0 ( T ) was computed according to eq 3 . The determination of the transport coefficient σ E 0 ( T ) then leads to the calculation of weighted mobility by where m e is the free electron mass and h is the Plank constant.…”

“…This challenging target might be achievable via the advancement of ceramic processing technologies and/or development of composites in which the secondary components (e.g., graphene) restrain grain growth, while facilitating the creation of oxygen vacancies at the GB. 6 , 7 , 22 , 40 , 43 …”

“… 9 Recently, interest has grown in the optimization and enhancement of thermoelectric properties of inorganic compounds via grain boundary (GB) engineering. 1 , 3 , 6 , 7 …”

“… 7 Generally, this single-crystal-like electrical conductivity at low temperature is attributed to the decrease in GB resistance with the reduction of the built-in potential barrier at the grain boundaries. 3 , 6 , 7 , 18 Localized changes in GB chemistry and structure (elementary composition, chemical state, etc.) are thought to be the primary reasons for the reduction of the potential barrier at the grain boundaries.…”

Robust Fabrication of Hybrid Lead‐Free Perovskite Pellets for Stable X‐ray Detectors with Low Detection Limit

“…[ 9,10,15 ] Nevertheless, grain boundaries in polycrystalline materials may critically limit their electronic performance, dramatically decreasing the carrier mobility by several orders of magnitude compared to SCs. [ 16 ] Hence, it will be more attractive for polycrystalline products if their electronic performance approaches that of SCs, which will favor PPs a promising alternative in X‐ray detection.…”