Reduction of thermal conductivity due to interfacial polarization mechanism of GaN/InxGa1-xNsuperlattice

The primary pyroelectric transition temperature of wurtzite nitrides (AlN, GaN and InN) has been explored theoretically from their thermal properties. The spontaneous and piezoelectric polarization modifies the thermal conductivity of nitrides. The thermal conductivity [Formula: see text] as a function of temperature including and excluding the polarization mechanism predicts a transition temperature [Formula: see text] between primary and secondary pyroelectric effects. Below [Formula: see text], thermal conductivity including polarization field [Formula: see text] is lesser than thermal conductivity excluding polarization field [Formula: see text]. This is due to negative thermal expansion in binary nitrides below [Formula: see text]; however, above [Formula: see text], [Formula: see text]. [Formula: see text] is significantly contributed by piezoelectric polarization above [Formula: see text] due to thermal expansion which is the reason for the secondary pyroelectric effect. The transition temperature [Formula: see text] for AlN, GaN and InN has been predicted as 100 K, 70 K and 60 K, respectively, which fit well with the prior literature studies. This report proposes that thermal properties’ study can reveal the role of acoustic phonons in pyroelectricity.

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Built-in-polarization field effect on intrinsic and extrinsic thermal conductivities of AlN/GaN/AlN quantum well

International Journal of Modern Physics B ◽

10.1142/s0217979215501490 ◽

2015 ◽

Vol 29 (21) ◽

pp. 1550149 ◽

Cited By ~ 2

Author(s):

A. Pansari ◽

V. Gedam ◽

B. K. Sahoo

Keyword(s):

Thermal Conductivity ◽

Relaxation Time ◽

Quantum Well ◽

Room Temperature ◽

Mean Free Path ◽

Polarization Field ◽

Polarization Mechanism ◽

Negative Effect ◽

Phonon Velocity ◽

Thermal Conductivities

In this paper, the effect of built-in-polarization field on lattice thermal conductivity of AlN/GaN/AlN quantum well (QW) has been theoretically investigated. The built-in-polarization field at the hetero-interface of GaN/AlN modifies elastic constant, phonon velocity and Debye temperature of GaN QW. The relaxation time of acoustic phonons (AP) in various scattering processes in GaN with and without built-in-polarization field has been computed at room temperature. The result shows that combined relaxation time of AP is enhanced by built-in-polarization field and implies a longer mean free path. The revised intrinsic and extrinsic thermal conductivities of GaN have been estimated. The theoretical analysis shows that up to a certain temperature the polarization field acts as negative effect and reduces the thermal conductivities. However, after this temperature both thermal conductivities are significantly contributed by polarization field. This gives the idea of temperature dependence of polarization effect which signifies the pyro-electric character of GaN. The intrinsic thermal conductivity at room temperature for with and without polarization mechanism is found to be 491 Wm -1 K -1 and 409 Wm -1 K -1, respectively i.e., 20% enhancement. However, the extrinsic thermal conductivity at room temperature for with and without polarization mechanism is found to be 280 Wm -1 K -1 and 245 Wm -1 K -1, respectively i.e., 13% enhancement. The method we have developed may be taken into account during the simulation of heat transport in optoelectronic nitride devices to minimize the self-heating processes and in polarization engineering strategies to optimize the thermoelectric performance of GaN alloys.

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Improving dielectric properties and thermal conductivity of polymer composites with CaCu3Ti4O12 and β-SiC hybrid fillers

Functional Materials Letters ◽

10.1142/s1793604715400111 ◽

2015 ◽

Vol 08 (03) ◽

pp. 1540011 ◽

Cited By ~ 4

Author(s):

Xin Ouyang ◽

Peng Cao ◽

Weijun Zhang ◽

Zhaohui Huang ◽

Wei Gao

Keyword(s):

Thermal Conductivity ◽

Dielectric Constant ◽

Dielectric Properties ◽

Dielectric Response ◽

Interfacial Polarization ◽

Melt Blending ◽

Hybrid Fillers ◽

Different Types ◽

Thermally Conductive ◽

Sic Whiskers

In this paper, we report a series of homogeneous polymeric composites with enhanced dielectric properties and thermal conductivity. The composites were constituted of polyvinylidene fluorides (PVDFs) matrix and CaCu 3 Ti 4 O 12 (CCTO) monolithic or CCTO/β- SiC hybrid fillers, and prepared by simple melt blending and hot moulding technique. The influence of different types of fillers and their composition on the dielectric response and thermal conductivity of the obtained composites was studied. Results show that hybrid loading is preferred and a reasonable combination of thermal conductivity (0.80 W⋅m-1⋅K-1), dielectric constant (∼50) and dielectric loss (∼0.07) at 103 Hz was achieved in the PVDF composite containing 40 vol.% CCTO and 10 vol.% β- SiC . The strong dipolar and interfacial polarization derived from the fillers are responsible for the enhancement of the dielectric constant, while the formation of thermally conductive networks/chains by β- SiC whiskers contributes to the improved thermal conductivity.

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A LABORATORY INVESTIGATION OF ELECTRICAL ANISOTROPY IN PRECAMBRIAN ROCKS

Geophysics ◽

10.1190/1.1440311 ◽

1972 ◽

Vol 37 (6) ◽

pp. 1022-1038 ◽

Cited By ~ 13

Author(s):

D. G. Hill

Keyword(s):

Dielectric Constant ◽

Interfacial Polarization ◽

Least Square ◽

Electrical Anisotropy ◽

Metamorphic Rocks ◽

Type Model ◽

Frequency Spectra ◽

Polarization Mechanism ◽

Northern Michigan

Laboratory electrical anisotropy measurements were made on selected dry metasediments and metavolcanics from the Precambrian complex of northern Michigan. Directional ac conductivity and dielectric‐constant values were obtained in six or more directions for each sample. These directional values were used to obtain a least‐square determination of the six independent coefficients needed to completely define the symmetric second‐rank, conductivity and dielectric constant tensors. Tensor principal values and directions were obtained from these coefficients. The results of this investigation indicate that metamorphic rocks may be characterized by strongly anisotropic electrical properties. The tensor representation surface symmetries reflect the symmetry of the rock fabric. Electrical anisotropy tends to increase, and the symmetry of the representation surfaces tends to decrease, at lower signal frequencies. The frequency spectra for all samples follow a relaxation‐type model, with critical frequencies occurring between 200 and 600 hz, indicating interfacial polarization as the dominant polarization mechanism.

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