arXiv subjects

Hirofumi Kakemoto

Publications and source records attributed to Hirofumi Kakemoto.

4 recordsLinked to original sources

arXiv2024

Colossal Seebeck coefficient of thermoelectric material calculated by space charge effect, and phonon drag background

Recently colossal Seebeck coefficient ($S$) has found in the several thermoelectric (TE) materials. We present colossal $S$ and large thermal electron motivate force (EMF) reproduced by space charge (SC) model, introducing multi-Debye lengths within grain boundaries (GBs) of TE materials with phonon drag (PD) effect accompanying with electron by electron-phonon interaction. In addition to $S$, the polarity reversal was also reproduced by transfer process with inner bias around SP generated from thermal EMF. Colossal $S$ and EMF for TE material were reproduced by inner SC model as a functions of averaged multi-Debye length within GBs.

cond-mat.mtrl-sci↗

arXiv2019

Theoretical specific heat, and thermal conductivity estimated by detailed phonon vibrations

We report the calculation results of specific heat ($c_v$), and thermal conductivity ($κ$) by using Einstein, and Debye models about rock salt (NaCl), oxides: Na$_x$CoO$_2$, SrTiO$_3$, and LiNbO$_3$. In calculation, the longitudinal (L), and transverse (T) sound velocities ($v_T$, $v_L$) were estimated from acoustic phonons' dispersion's (~$ω$/$K$) in above materials, and the average sound velocities ($v_a$) were input into Debye model for $κ$ equation, and results were compared with that of Einstein model. In some oxides, $v_a$ is relatively reduced at slight high $v_T$ ($v_T$/$v_L$=0.3-0.5). The relation of $κ$, $v_a$ and $T$ were imaged as the contour plots about realizing low $κ$ values to be application of thermoelectric properties.

cond-mat.mtrl-sci↗

arXiv2019

Thermoelectric enhanced ZT regime calculated by Fermi integral method

We report about detailed dimensionless figure of merit ($ZT$) calculated by using Fermi integral method (compared with Bi$_2$Te$_3$, CoSb$_3$, and SrTiO$_3$) for thermoelectric (TE) materials' design and its module application. Particularly, TE properties: electrical conductivity (small polaron: $σ$($m$*)), Seebeck coefficient ($S$), thermal conductivity ($κ_e$), and $ZT$ were calculated by using reduced energy ($ζ$=$E$/$k_B T$), as the functions of $T$, and effective mass ($m$*/$m$). Enhancement of $ZT$ was investigated by contour plots of $T$, and $m$*/$m$ versus $ζ$.

cond-mat.mtrl-sci↗

arXiv2017

Theoretical calculation of transport properties of oxide material using narrow band model

We report about the results of theoretical calculations of temperature dependence of resistivity ($ρ$) and Seebeck coefficient ($S$) for thermoelectric (TE) and superconductivity (SC) phases by arithmetic equations based on narrow band model with oxygen deficient structure, as the functions of band-filling degree ($F$), and band width ratio of electron and spin states ($W$σ/$W$D). The phase diagrams of TE and SC states, and boundary were imaged to the properties of $ρ$ and $S$ as a function of $F$ and $W$σ/$W$D.

cond-mat.mtrl-sci↗