Hongzhang Song

Improved thermoelectric properties of hole-doped Bi2−xNaxBa2Co2Oy ceramics

In this work, Bi2−xNaxBa2Co2Oy (x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) ceramic samples were prepared by the conventional solid phase method. The influence of Na element doping on the thermoelectric properties of samples was investigated from 300 K to 950 K. Compared with undoped sample, the Seebeck coefficients of Na-doped samples have only a slight decrease. While, the electrical resistivity of the Na-doped samples reduces, for Bi2−xNaxBa2Co2Oy ceramic samples with x ≤ 0.15, the electrical resistivity decreases with increasing Na doping amounts due to the hole-doping effect. In addition, its temperature-dependent resistivity exhibits metallic electrical conductivity behavior. While, the samples with x > 0.20 exhibit semiconductor electrical conductivity behavior at the temperature range of 473–823 K, because of the significant reduction of the electrical resistivity and the slight decrease of Seebeck coefficients, the power factors of the doped samples get a significant improvement. For the most suitable doped sample Bi1.8Na0.2Ba2Co2Oy, its ZT value can reach a better value of 0.2 at 873 K.

Thermoelectric properties of rare earth-doped n-type Bi2Se0.3Te2.7 nanocomposites

Abstractn-Type R0.2Bi1.8Se0.3Te2.7 (R = Ce, Y and Sm) nanopowders were synthesized by hydrothermal method and the thermoelectric properties of the bulk samples made by hot-pressing these nanopowders were investigated. The Ce, Y and Sm doping have significant effects on the morphologies of the synthesized nanopowders. The thermoelectric property results show that Ce, Y and Sm doping not only help to decrease the electrical resistivity, but also help to reduce the thermal conductivity. Among rare earth elements-doped samples, it seems that the Y0.2Bi1.8Se0.3Te2.7 bulk has a suitable microstructure, which scatters phonons effectively but does not scatter electronic carriers as much. As a result, the ZT values of Y0.2Bi1.8Se0.3Te2.7 can reach 1.21 at 413 K, which is higher than those of Bi2Se0.3Te2.7 ingots made by zone-melting method.

Thermoelectric properties of Cu2Se/xNi0.85Se hot-pressed from hydrothermal synthesis nanopowders

The Cu2Se/xNi0.85Se (x = 0, 0.025, 0.05, 0.075, 0.1, 0.15, 0.2, 0.3, 0.4 and 0.5) nanopowders were synthesized by the hydrothermal method and then were hot-pressed into bulk alloys. The effects of Ni0.85Se secondary phase on the thermoelectric (TE) properties of Cu2Se were investigated. For x = 0.025 and x = 0.05, both their electrical resistivity and Seebeck coefficients increase. While for x ≥ 0.075, they decrease instead. The samples for x ≤ 0.075 have lower thermal conductivity. However, for x ≥ 0.1, the thermal conductivity rises remarkably. As an overall result, the maximum value of dimensionless TE figure of merit (ZT) reaches 1.52 at 873 K for the sample of x = 0.05, 36.5% higher than for the sample without Ni0.85Se.

Enhanced thermoelectric properties of Hg-doped Cu2Se

The Cu2−xHgxSe (x = 0, 0.05, 0.10 and 0.15) nanopowders were fabricated using the hydrothermal synthesis, and then hot-pressed into bulk alloys. The effects of Hg doping on the thermoelectric (TE) properties of Cu2Se were investigated. The electrical resistivities of all the doped samples are lower than that of the nondoped sample due to the induced cation vacancies. For the x = 0.10 and x = 0.15 samples, Seebeck coefficients increase slightly compared with the nondoped sample at higher temperature. Except for the sample of x = 0.05, the thermal conductivities of x = 0.10 and x = 0.15 samples are substantially lower than that of the x = 0.00 sample. As an overall result, the maximum value of ZT, which is the dimensionless TE figure of merit, reaches 1.50 at 600∘C for the x = 0.10 sample.

Thermoelectric properties of hole-doped Yb1-xPbxBaCo4O7+δ ceramics

The effects of Pb doping on the thermoelectric (TE) properties of Yb1-xPbxBaCo4O7+δ (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) ceramic samples prepared by the solid-state reaction method were investigated from 383 K to 973 K. The results showed that with increase of the Pb content, the electrical resistivity decreased remarkably, meanwhile the Seebeck coefficient decreased slightly, resulting in an enhancement of the power factor (PF). The effect of Pb doping on the thermal conductivity was insignificant. According to the PF and the dimensionless figure of merit (ZT) value, the optimum Pb doping content was x = 0.08. The ZT value reached 0.12 at 973 K, being 69.5% higher than that of the sample without Pb doping.

High temperature thermoelectric properties of Bi2−xNaxSr2Co2Oy ceramics

The Na doping effects on the high temperature thermoelectric properties of Bi2−xNaxSr2Co2Oy (x = 0, 0.05, 0.10, 0.15, 0.20 and 0.30) ceramics were investigated from 343 K to 973 K. When x ≤ 0.15, the electrical resistivity of Bi2−xNaxSr2Co2Oy decreases with increasing Na doping amount due to the hole-doping effect, which exhibits metallic electrical conductivity behavior. While, at the temperature range of 480–830 K, the samples with x > 0.20 exhibit semiconductor electrical conductivity behavior instead. The Seebeck coefficients are improved by Na doping at lower temperature, but they decrease slightly at higher temperature except for x = 0.2. Roughly, the thermal conductivity is depressed by the doping defects. As an overall result, the dimensionless figure of merit (ZT) of Bi1.8Na0.2Sr2Co2Oy reaches the maximum value of 0.3 K at 973 K, which is nearly twice the value of the undoped sample LBFSx.

Enhanced thermoelectric properties of the hole-doped Bi2−xKxSr2Co2Oy ceramics

In this paper, the influence of K element doping on the thermoelectric properties of the Bi2−xKxSr2Co2Oy (x = 0.00, 0.05, 0.10, 0.15, and 0.20) samples prepared by the solid-state reaction method were investigated from 333 K to 973 K. It was shown that due to the p-type K doping the electrical resistivity of the doped sample can be reduced remarkably as compared with the undoped sample, especially for the optimum doped sample Bi1.9K0.1Sr2Co2Oy. The Seebeck coefficients of the K doped samples have only a slight decrease as compared with the undoped sample. As a result of the remarkable reduction of the electrical resistivity the power factor of the doped sample have a significant improvement. The thermal conductivity of the samples is depressed due to the defects caused by K doping. As an overall result, the dimensionless figure of merit (ZT) of the Bi1.9K0.1Sr2Co2Oy sample reaches a maximum value of 0.3 at 973 K, being 93% higher than that of the undoped sample.

Investigation on Oxygen Resistance Properties of RBaCo 2 O 5+δ Ceramics: Investigation on Oxygen Resistance Properties of RBaCo 2 O 5+δ Ceramics

用固相反应法制备了RBaCo 2 O 5+ δ (R=Y、Dy、Gd、Pr、Nd、Sm和Eu)系列陶瓷. 用标准四探针法测量了它们从室温到600℃之间的电阻率变化. 在温度较低时, 它们的电阻率都随着温度的升高而减小, 显示为半导体特征. 当电阻率在某一温度达到最大值后, 电阻率开始随着温度升高而缓慢增加, 显示为半金属特征. 进一步研究了RBaCo 2 O 5+ δ 系列陶瓷在高温恒温时的电阻率随着环境气氛的变化情况. 结果表明RBaCo 2 O 5+ δ 陶瓷是一类潜在的氧阻传感器材料, 并且它们的响应速率从快到慢顺序是YBaCo 2 O 5+ δ > DyBaCo 2 O 5+ δ > GdBaCo 2 O 5+ δ > PrBaCo 2 O 5+ δ > NdBaCo 2 O 5+ δ > SmBaCo 2 O 5+ δ > EuBaCo 2 O 5+ δ . 以YBaCo 2 O 5+ δ 陶瓷为例, 在700℃恒温时, 当从氧气氛切换到氮气氛时, 由于晶格中氧的脱附导致电阻率先是快速上升, 然后缓慢上升, 并在90 s内达到最大平衡值. 反之, 当从氮气氛切换为氧气氛时, 由于氧的吸附, 电阻率迅速降低, 约30 s内达到最小平衡值.用固相反应法制备了RBaCo 2 O 5+ δ (R=Y、Dy、Gd、Pr、Nd、Sm和Eu)系列陶瓷. 用标准四探针法测量了它们从室温到600℃之间的电阻率变化. 在温度较低时, 它们的电阻率都随着温度的升高而减小, 显示为半导体特征. 当电阻率在某一温度达到最大值后, 电阻率开始随着温度升高而缓慢增加, 显示为半金属特征. 进一步研究了RBaCo 2 O 5+ δ 系列陶瓷在高温恒温时的电阻率随着环境气氛的变化情况. 结果表明RBaCo 2 O 5+ δ 陶瓷是一类潜在的氧阻传感器材料, 并且它们的响应速率从快到慢顺序是YBaCo 2 O 5+ δ > DyBaCo 2 O 5+ δ > GdBaCo 2 O 5+ δ > PrBaCo 2 O 5+ δ > NdBaCo 2 O 5+ δ > SmBaCo 2 O 5+ δ > EuBaCo 2 O 5+ δ . 以YBaCo 2 O 5+ δ 陶瓷为例, 在700℃恒温时, 当从氧气氛切换到氮气氛时, 由于晶格中氧的脱附导致电阻率先是快速上升, 然后缓慢上升, 并在90 s内达到最大平衡值. 反之, 当从氮气氛切换为氧气氛时, 由于氧的吸附, 电阻率迅速降低, 约30 s内达到最小平衡值.RBaCo2O5+δ (R=Y, Dy, Gd, Pr, Nd, Sm, and Eu) ceramics were synthesized by the solid-state reaction method. Their resistivities depending on temperature were investigated by the standard four-probe method from room temperature to 600°C. At low temperature, all the resistivities decrease with the rising temperature, and exhibit semiconducting behavior. After the resistivities reach minimum values at certain temperatures, they increase slowly with temperature, and exhibit semimetal conducting behavior. Especially, the resistivity variations of RBaCo2O5+δ samples with the change of atmosphere at constant temperatures are studied. The results show that RBaCo2O5+δ could be potential oxygen resistance sensor materials, and that the responding rates of RBaCo2O5+δ are YBaCo2O5+δ > DyBaCo2O5+δ > GdBaCo2O5+δ > PrBaCo2O5+δ > NdBaCo2O5+δ > SmBaCo2O5+δ > EuBaCo2O5+δ. For YBaCo2O5+δ, the resistivity rises quickly due to the oxygen desorption when the atmosphere is switched from oxygen to nitrogen at 700°C, and reaches its maximum equilibrium value within 90 s. In addition, the resistivity drops drastically due to the oxygen adsorption when the nitrogen atmosphere is switched to oxygen, and reaches its minimum equilibrium value within 30 s.

Influence of R3+ ion sizes on the thermoelectric properties of RBaCo4O7+δ ceramics

The influence of R3+ ion sizes on the electrical resistivity, Seebeck coefficients, thermal conductivity and ZT values of RBaCo4O7+δ prepared by the solid-state reaction method was investigated from 373 K to 973 K. The electrical resistivity decreases with decreasing R3+ ion sizes. Both the electrical resistivity and the Seebeck coefficients have a transition at about 630 K. Especially, the transition phenomenon disappears gradually with decreasing R3+ ion sizes, and is attributed to the oxygen adsorption of RBaCo4O7+δ. The ZT values increase with rising temperature or decreasing R3+ ion sizes. The InBaCo4O7+δ with the smallest R3+ size has the maximum ZT value that reaches 0.1 at 973 K.