Electric-Field-Dependent Thermal Conductivity in Fresh and Aged Bulk Single Crystalline $\mathrm{BaTiO_3}$

TL;DR

Problem: enabling active, room-temperature thermal switching in bulk ferroelectrics for thermal management. Approach: combine a steady-state in-situ electric field platform, TDTR measurements, and first-principles finite-temperature lattice dynamics to study bulk BaTiO3 under aging. Findings: switching is dominated by domain-configuration–dependent phonon transport rather than strain, and aging via defect dipoles substantially enhances switching contrast, nearly doubling the modulation in aged samples. Significance: defect-domain engineering provides a practical route to robust, electrically tunable heat transport and opens a platform for exploring field-driven phase behavior in bulk ferroics.

Abstract

Active thermal management requires advances in thermal switching materials, whose thermal conductivity responds to external stimuli. The electric field, as one of the most convenient and effective stimuli, has shown great potential in tuning the thermal conductivity of ferroelectric materials. While previous studies on electric-field-induced ferroelectric thermal switching have primarily focused on thin films and bulk solid solutions with strong extrinsic interface and defect scatterings, bulk single crystals, which can offer clear insights into intrinsic thermal switching mechanisms, have received comparatively less attention. Here, we demonstrate electric-field-induced thermal switching in bulk single-crystalline $\mathrm{BaTiO_3}$ (BTO) at room temperature and elucidate the critical role of domain evolution and aging in governing heat transport. Using a customized steady-state platform with in-situ electric fields up to $\pm$10 kV/cm, we observe a modulation of thermal conductivity up to 35% in fresh BTO driven by polarization reorientation and domain restructuring. First-principles finite-temperature lattice-dynamics calculations confirm that the switching behavior primarily originates from anisotropic phonon transport associated with domain configuration rather than strain-induced changes in phonon velocities. We further reveal that both ambient aging and controlled thermal aging can enhance the switching contrast through the formation and alignment of defect dipoles that modulate phonon-defect scattering. These results establish defect-domain interactions as a powerful design parameter for ferroelectric thermal switches and demonstrate a versatile experimental platform for exploring field-tunable heat transport and phase behavior in bulk functional materials.

Figures (5)

• Figure 1: Steady-state thermal conductivity measurements of fresh BaTiO$_3$ single crystals with in-situ electric fields. (a) The schematic and (b) a picture of the steady-state experimental setup. (c) The schematic showing the ferroelectric polarization as a function of electric field in BTO. Here, the polarization represents the out-of-plane component. The temperature gradient is applied along the in-plane direction, while the electric field is applied along the out-of-plane direction. (d) Thermal conductivity in a fresh BTO single crystal as a function of the external electric field during the first scan.
• Figure 2: Calculated thermal conductivity of BTO at 300 K using first-principles finite-temperature lattice dynamics. (a) The crystal structure of BTO indicating the out-of-plane (z) and in-plane (xy) directions, where Ti off-centering is highlighted. (b) Calculated phonon dispersion of the tetragonal phase of BTO at 300 K, showing a stabilized lattice by phonon anharmonicity. (c) The calculated thermal conductivity along the polarization direction ($\kappa_z$) and perpendicular to the polarization direction ($\kappa_{xy}$) in BaTiO$_3$ at 300 K as a function of strain (-1 to 1%). A positive (negative) sign indicates a tensile (compressive) strain along the polarization direction. (d) The cumulative thermal conductivity of BTO at 300 K as a function of phonon mean free path.
• Figure 3: Electric-field-dependent thermal conductivity in time-aged BaTiO$_3$(100) single crystals. The thermal conductivity perpendicular to the polarization direction ($\kappa_{xy}$) in BaTiO$_3$ at 300 K as a function of electric fields during (a) the first and (b) the second scan. The initial increase in thermal conductivity during the first scan is attributed to the polarization switch from in-plane to out-of-plane direction. (c)The polarization-electric field (P-E) hysteresis loop and (d) the strain–electric field (S-E) hysteresis loop of the time-aged BaTiO$_3$ single crystal.
• Figure 4: Electric-field-dependent thermal conductivity in heat-aged BaTiO$_3$ (001) sample. The thermal conductivity of the heat-aged sample during (a) the first and (b) the second scan of the electric field. The asymmetric thermal switching in the first scan is attributed to the defect dipoles formed during the aging process. (c)The polarization-electric field (P-E) hysteresis loop and (d) the strain–electric field (S-E) hysteresis loop of the heat-aged sample.
• Figure 5: Raman spectra of fresh and heat-aged BaTiO$_3$. The Raman spectra after baseline-correction probed from (a) a single ferroelectric domain and (b) multi domains. (c) Full-width-half-maximum (FWHM) of the main peaks and (d) LO-TO splitting probed from a single domain, more domains (two to three domains), and multiple domains.