Jichao Li

High piezoelectric properties and domain configuration in BaTiO3 ceramics obtained through solid-state reaction route

The reported data for average grain size g and average domain width w are incorrect in the previously published version. They should be multiplied by a factor of 2. The abstract should therefore be corrected to read as: ... at around 480 nm with the decrease in the grain size from 19 to 4.0 μm. The text on page 3, right column, should read as: line 7: its g value is 19 μm line 10: at g=7 μm line 20: at around 480 nm noindent line 48: g values ranging from 19 to 4.0 μm and on page 4, right column, should read as: line 1: g ≥ 7 μm and g < 7 μm. The bar scales in the previously published figure 2 are corrected by a factor of 2. The horizontal scale of average grain size g and the right-hand scale of average domain width w in the previously published figure 3 are both corrected by a factor of 2. These corrections affect no other part of the article. Corrected versions of figures 2 and 3 are included in the associated PDF file.

Vibrational mode analysis of β-phase poly(vinylidene fluoride)

The infrared spectrum of β-phase poly(vinylidene fluoride) (PVDF) film (30 μm) in the region from 4000 to 400u2009cm−1 has been measured. The vibrational frequencies of all-trans chains of PVDF have been calculated from first principles based on a restricted Hartree–Fock self-consistent field method. The calculated result is in good agreement with the experiment. All the vibrational modes were divided into three types, only one of them which is in the region from 1330 to 1020u2009cm−1, corresponds to a changing dipole moment, and may be responsible for the spontaneous polarization.

A study of the vibrational and thermoelectric properties of silicon type I and II clathrates

First principles calculations are employed to investigate both type I and II silicon clathrates. The phonon and infrared spectra of both types of clathrate are obtained. We find a localized vibrational mode of Si46 whose frequency is 375.0u2002cm−1, where the vibration in the mode localizes in the hexagonal chain. The heat capacity of both clathrates is the same as that of the diamond phase Si (d-Si). When the temperature is lower than 100 K, the Debye temperatures of the clathrates are higher than that of d-Si; however, the Debye temperatures of both clathrates at high temperature (>100u2002K) are lower than that of the d-Si. The mean free paths (λ) and thermal conductivities (κ) of the clathrates are larger than those of d-Si at low temperature. The Seebeck coefficients (S) of the clathrates are higher than that of d-Si in the temperature interval 300–1000 K; however, both clathrates exhibit a lower value of σ/τ when compared to the d-Si.

IR VIBRATIONAL MODES OF PVDF CHAINS

The vibration frequencies of all-trans chains of β-PVDF have been calculated using first-principles calculations. The obtained frequency spectrum is fairly in agreement with the infrared spectrum of PVDF film. The vibrational modes, with wave-numbers ranges between 1330cm -1 and 1020 cm -1 , might be responsible for the spontaneous polarization.

Effects of fluorine doping on thermoelectric properties of Sr0.61Ba0.39Nb2O6 ceramics

The thermoelectric properties of Sr0.61Ba0.39Nb2O6 ceramics, doped with different contents of fluorine at the oxygen sites, were investigated in the temperature range of 323 to 1073 K. The electrical resistivity is reduced significantly after fluorine doping. However, the magnitudes of electrical resistivity, Seebeck coefficient (S), and slope of S at high temperatures (dS/dT) vary non-monotonically with increasing doping contents, indicating that doped fluorine ions not only act as electron donors, but also influence band structure. The lattice thermal conductivity decreases when fluorine ions are slightly doped, and increases with increasing fluorine content because of the increasing average grain size. The thermoelectric performance is enhanced by slight fluorine doping due to the increase of the power factor and the reduction of thermal conductivity. The thermoelectric figure of merit reaches maximum value (0.21 at 1073 K) in the Sr0.61Ba0.39Nb2O5.95F0.05 sample.

Improvement of thermoelectric properties and their correlations with electron effective mass in Cu1.98SxSe1−x

Sulphur doping effects on the crystal structures, thermoelectric properties, density-of-states, and effective mass in Cu1.98SxSe1−x were studied based on the electrical and thermal transport property measurements, and first-principles calculations. The X-ray diffraction patterns and Rietveld refinements indicate that room temperature Cu1.98SxSe1−x (xu2009=u20090, 0.02, 0.08, 0.16) and Cu1.98SxSe1−x (xu2009=u20090.8, 0.9, 1.0) have the same crystal structure as monoclinic-Cu2Se and orthorhombic-Cu2S, respectively. Sulphur doping can greatly enhance zT values when x is in the range of 0.8≤u2009×u2009≤1.0. Furthermore, all doped samples show stable thermoelectric compatibility factors over a broad temperature range from 700 to 1000u2009K, which could greatly benefit their practical applications. First-principles calculations indicate that both the electron density-of-sates and the effective mass for all the compounds exhibit non-monotonic sulphur doping dependence. It is concluded that the overall thermoelectric performance of the Cu1.98SxSe1−x system is mainly correlated with the electron effective mass and the density-of-states.

Enhanced piezoelectricity in plastically deformed nearly amorphous Bi12TiO20-BaTiO3 nanocomposites

Bulk Bi12TiO20-BaTiO3 (BTO-BT) nanocomposites are fabricated through the high-temperature interfacial reaction between nanometer-sized BaTiO3 particles and melting Bi12TiO20. Although the obtained BTO-BT nanocomposites are nearly amorphous and display very weak ferroelectricity, they exhibit relatively strong piezoelectricity without undergoing the electrical poling process. The volume fraction of crystalline Bi12TiO20 is reduced to less than 10%, and the piezoelectric constant d33 is enhanced to 13 pC/N. Only the presence of the macroscopic polar amorphous phases can explain this unusual thermal stable piezoelectricity. Combining the results from X-ray diffraction, Raman spectroscopy, and thermal annealing, it can be confirmed that the formation of macroscopic polar amorphous phases is closely related to the inhomogeneous plastic deformation of the amorphous Bi12TiO20 during the sintering process. These results highlight the key role of plastically deformed amorphous Bi12TiO20 in the Bi12TiO20-based pola...

Enhanced Thermoelectric Response of Ca0.96Dy0.02Re0.02MnO3 Ceramics (Re = La, Nd, Sm) at High Temperature

Perovskite-type Ca0.98Dy0.02MnO3, Ca0.96Dy0.04MnO3, and Ca0.96Dy0.02 Re0.02MnO3 (Rexa0=xa0La, Nd, Sm) were prepared by solid-state reaction, and their thermoelectric properties were evaluated between 300 and 1000xa0K. All were single-phase, with an orthorhombic structure, and had metal-like temperature dependence of resistivity and Seebeck coefficient. The second doping element, Rexa0=xa0La, Nd, or Sm, introduced a larger carrier concentration, leading to a decrease in both resistivity and Seebeck coefficient. This contributed to lower thermal conductivity by introducing a second element into the system. The highest figure of merit, 0.20, was obtained for Rexa0=xa0La at 973xa0K; this was an increase of almost 100% compared with Ca0.98Dy0.02MnO3 at the same temperature.

Dopant position in Ti-doped high-temperature phase Ta2O5: First principles study

The ab initio calculation and bond valence model (BVM) are employed to investigate dopant occupancy in the Ti-doped high-temperature phase Ta2O5. In this structure, there are two types of Ta atoms, which the authors denote as Ta1 locating inside oxygen octahedral and Ta2 locating inside oxygen decahedral. The 5d state electron configuration of Ta1 and Ta2 is different, the hybridization between Ta1 5d state and O 2p state is stronger than that between Ta2 and O. The chemical bonding between Ta and oxygen ions is mainly covalent. However, there is an increase of the covalent character in going from Ta1–O bond to Ta2–O bond. Both total energy method and BVM indicate that Ti substituting Ta1 is energy favorable, and this maybe due to different electronic structures of Ta1 and Ta2.

ELECTRONIC STRUCTURE OF RELAXOR PMN

ABSTRACT We perform density functional theory method to study the electronic structure of relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3. An ordered perovskite structure based supercell was examined with the B sites Nb-Mg-Nb stacking along the [001] direction. Band structure, density of states and electron density have been obtained. The calculated band gap is a direct one with the value of 1.05 eV. It is found that the Mg-O bond presents no covalency, whereas there is a considerable Nb-O covalent bonding. The different B-O bonding characters might be responsible for the relaxor properties of Pb(Mg1/3Nb2/3)O3 crystal.