Conducting polymers are potential candidates for thermoelectric (TE) applications owing to their low thermal conductivity, non-toxicity and low cost. However, the coil conformation and random aggregation of polymer chains usually degrade electrical transport properties, thus deteriorating TE performance. In this work, we fabricated poly(3-hexylthiophene) (P3HT) films with highly oriented morphology using 1,3,5-trichlorobenzene (TCB), an organic small-molecule, as a template for polymer epitaxy under a temperature gradient crystallization process. The resulting P3HT molecules, which were confirmed to be highly anisotropic by a combination of scanning electron microscopy, atomic force microscopy, polarizing microscope, polarized Raman spectroscopy, and two-dimensional-grazing incidence X-ray diffraction (GIXRD) analysis, not only markedly reduced the conjugated defects along the polymer backbone, but also effectively increased the degree of electron delocalization. These combined phenomena produced an efficient, 1D path for carrier movement and therefore resulted in enhanced carrier mobility in the TCB-treated P3HT films. The maximum values of the electrical conductivity and Seebeck coefficient were 320 S cm À1 and 269 μV K À1 , respectively. Consequently, the maximum TE power factor and ZT value at 365 K reached 62.4 μW mK À2 and 0.1, respectively, in the parallel direction of the TCB-treated P3HT film. To the best of our knowledge, these are the highest values reported for pure P3HT TE materials. The method of using organic small-molecule epitaxy to generate highly anisotropic polymer films is expected to be valid for many conducting polymers.
high thermal conductivity are widely used in heat dissipating applications, [3][4][5][6] while the materials with low thermal conductivity [7][8][9][10] are used as thermal insulation. In particular, thermal conductivity is one of the key parameters in thermoelectric materials and also plays an important role in other energy materials such as solar cells and battery materials. Therefore, evaluation of thermal conductivity is very fundamental and important, but the measurement could sometimes be a great challenge. The understanding and measurement of thermal conductivity are especially questionable for materials with phase transitions while these materials exist extensively and have been exploited for different fields including thermoelectrics, [11][12][13][14] solid state memory, [15] and switches. [16] The energy exchange during phase transitions gives rise to a few fundamental questions on thermal conductivity measurement. Transient measurement methods such as laser flash method (LFA) are commonly used to measure thermal diffusivity λ and the thermal conductivity κ is calculated using the equation of κ = C P × d × λ (d is the density and C P is the heat capacity), due to the significant advantages of transient methods over the steady-state measurements. [17] It is well known that the heat capacity (C P ) can be significantly increased during phase transition because the extra energy is required to transit a low temperature structure to a high temperature structure in materials (see Figure 1a). Recent study also shows that the thermal diffusivity (λ) can be lowered in some phase transition materials such as Cu 2 Se, Cu 2 S, and Ag 2 S, but is almost unaffected by phase transition in Ag 2 Se (see Figure 1b). The understanding on thermal conductivity during phase transitions is not established yet. This leads to the thermal conductivity calculated with different heat capacity values highly deviated, although the measured heat capacity and thermal diffusivity are quite close or similar. For example, a dramatic decrease in κ in Cu 2 Se second-order phase transition is reported by Liu et al. [11] when using the Dulong-Petit value for heat capacity, while an increased κ is reported by Brown et al. [18] after adding the contribution of phase transition to heat capacity (Figure 1c). Such different κ values change the thermoelectric figure of merit (zT) from a moderate value of 0.6 to an extremely high value of 2.3 (which can be considered as a breakthrough in thermoelectrics) in Cu 2 Se during its second-order phase transition. More confusingly, the heat capacity ( Figure 1a) and electrical transport measurements ( Figure S6, Supporting Information) clearly show that Cu 2 S and Ag 2 S have first-order phase transitions with Thermal conductivity is a very basic property that determines how fast a material conducts heat, which plays an important and sometimes a dominant role in many fields. However, because materials with phase transitions have been widely used recently, understanding and measuring temperature-dependent t...
Pure polyaniline (PANI) films with different molecular chain packing states were successfully prepared by simply tuning the m-cresol content in the solvent.
A novel bismuth-based material of hot-pressed (Bi0.5K0.5)TiO3–0.06La(Mg0.5Ti0.5)O3 ceramic with an ultrahigh energy storage density and fast discharge speed.
Lead-free (1−x)(0.8Bi0.5Na0.5TiO3-0.2SrTiO3)-xNaNbO3 (x = 0–0.1, abbreviated as BNT-ST-xNN) ceramics were fabricated by a conventional sintering route with pure perovskite phase via XRD analysis. Raman spectrum was exploited in order to give an insight into the variation of local structural evolution. All compositions exhibited an obvious evolution of dielectric relaxation behaviors. Dielectric and ferroelectric properties clarified that a crossover from nonergodic to ergodic relaxor properties was obtained with the addition of NN content. A relatively large energy storage density was obtained WRec ∼ 0.74 J/cm3 at 7 kV/mm for x = 0.05 at room temperature. Particularly, the energy storage properties exhibited temperature (25–160 °C) and frequency stability (0.1–20 Hz) with WRec around 0.6 J/cm3 at 6 kV/mm for x = 0.05 within the ergodic region. Pulsed discharging current waveforms were measured under different electric fields to detect the energy storage density and discharging speed behavior. An illustration of the charge-discharge process for the nonergodic and ergodic relaxor was depicted in order to disclose the difference of energy storage properties in BNT-ST-xNN system, and it is believed that this concept can be a guideline for fixing a position when designing a new energy-storage system for BNT-based relaxor ferroelectric ceramics.
Polarization field engineering of piezoelectric materials is considered as an advisable strategy in fine‐tuning photocatalytic performance which has drawn much attention recently. However, the efficient charge separation that determines the photocatalytic reactivities of these materials is quite restricted. Herein, a judicious combination of piezoelectric and photocatalytic performances of BiOX/BaTiO3 (X = Cl, Br, Cl0.166Br0.834) to enable a high piezophotocatalytic activity is demonstrated. Under the synergic advantages of chemical potential difference and piezoelectric potential difference in BiOX/BaTiO3 composites, the photoinduced carriers recombination is largely halted, which directly contributes to the significantly promoted piezophotocatalytic activity of piezoelectric composites. Inspiringly, the BiOBr/BaTiO3 composites under light irradiation with auxiliary ultrasonic activation result in an ultrahigh and stable photocatalytic performance, which is much higher than the total of those by isolated photocatalysis and piezocatalysis, and can rival current excellent photocatalytic system. In fact, the theoretical piezoelectric potential difference of BiOBr/BaTiO3 composites reaches 100 mV, which far exceeds the pure BaTiO3 of 31.21 mV and BiOBr of 30 mV, respectively. First, fabrication of BiOX/BaTiO3 piezoelectric composites and its remarkable piezophoto coupling catalysis behavior lays new ground for developing high‐efficiency piezoelectric photocatalysts in purifying wastewater, killing bacteria, and other piezophototronic processes.
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