Ferroelectricity in Dion–Jacobson ABiNb2O7(A = Rb, Cs) compounds

The ferroelectric properties of 2-layer Dion–Jacobson compounds ABiNb2O7 (A = Rb and Cs) were studied. Ferroelectricity and piezoelectricity of CsBiNb2O7 were demonstrated for the first time. The ferroelectric domain structure of Dion–Jacobson compounds were imaged using PFM. The Curie points of RbBiNb2O7 and CsBiNb2O7 are 1098 ± 5 and 1033 ± 5 °C, respectively. The piezoelectric constant of RbBiNb2O7 and CsBiNb2O7 are approximately 5 and 8 pC N−1. Thermal depoling was also studied to confirm the Curie temperature and the stability of the piezoelectricit

Investigation of the Microstructural and Thermoelectric Properties of the (GeTe)0.95(Bi2Te3)0.05 Composition for Thermoelectric Power Generation Applications

In the frame of the current research, the p-type Bi2Te3 doped (GeTe)(0.95)(Bi2Te3)(0.05) alloy composed of hot pressed consolidated submicron structured powder was investigated. The influence of the process parameters (i.e., powder particles size and hot pressing conditions) on both reduction of the lattice thermal conductivity and electronic optimization is described in detail. Very high maximal ZT values of up to similar to 1.6 were obtained and correlated to the microstructural characteristics. Based on the various involved mechanisms, a potential route for further enhancement of the ZT values of the investigated composition is proposed.EC, FP7 PowerDriver Projec

Effect of spark plasma sintering on the structure and properties of Ti1-xZrxNiSn half-heusler alloys

XNiSn (X = Ti, Zr and Hf) half-Heusler alloys have promising thermoelectric properties and are attracting enormous interest for use in waste heat recovery. In particular, multiphase behaviour has been linked to reduced lattice thermal conductivities, which enables improved energy conversion efficiencies. This manuscript describes the impact of spark plasma sintering (SPS) on the phase distributions and thermoelectric properties of Ti0.5Zr0.5NiSn based half-Heuslers. Rietveld analysis reveals small changes in composition, while measurement of the Seebeck coefficient and electrical resistivities reveals that all SPS treated samples are electron doped compared to the as-prepared samples. The lattice thermal conductivities fall between 4 W·m−1·K−1 at 350 K and 3 W·m−1·K−1 at 740 K. A maximum ZT = 0.7 at 740 K is observed in a sample with nominal Ti0.5Zr0.5NiSn composition

Perovskite-like layered structure A2B20 & ferroelectrics with super-high Curie points

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Lanthanum and strontium modified bismuth ferrite based perovskites with ultra-narrow band gaps

The wide optical band gaps of ferroelectric perovskite oxides have restricted their light absorbing capacities in the photovoltaic devices. In this work, an ultra-narrow band gap E _g and wide optical absorption across the ultraviolet-visible-infrared sunlight spectrum was achieved in lanthanum and strontium atoms modified Bi(Fe, Mn)O _3 perovskites by chemical substitution and defect engineering. XRD results show that the A and B site co-substituted samples are single phase. The XPS characterizations indicate the Fe ions are in the trivalent state for all the samples. The LM6 and SM6 samples exhibit an ultra-narrow band gap about 1.26 eV and 1.06 eV, respectively. The reduced E _g was due to the defect states produced within the band gap, acting as a scaffold to give electrons to Fe 3d states and receive the electrons from O 2p states. Based on this research, these chemically modified BFO based perovskite could potentially extend its sunlight absorption deep into the infrared region

Optical bandgap tuning of ferroelectric semiconducting BiFeO3-based oxide perovskites via chemical substitution for photovoltaics

Ferroelectrics exhibit bulk photovoltaic effect, of which spontaneous electric polarization separates photo-excited carriers and results in above-bandgap open-circuit voltage. Compared with organometal halide perovskites, ferroelectric oxide perovskites are much more stable in a wide range of mechanical, chemical and thermal conditions and able to fabricate using low-cost facilities. The bottlenecks for ferroelectric photovoltaic applications are their poor optical absorption of visible light and high electric resistivity owing to wide bandgap. In this work, bandgap of BiFeO3-based oxide perovskites was judiciously tuned in a range of 1.10-2.06 eV through B-site chemistry, which makes ferroelectric semiconducting oxide perovskites feasible for photovoltaic solar cell applications with wide light absorption and high efficient energy conversion. In particular, La and Mn co-substituted BiFeO3 solid solution exhibits a narrow direct bandgap around 1.20 eV, which extends photon absorptions over ∼80% sunlight spectrum covering ultraviolet-visible-infrared region and increases electrical conductivity (σdc) up to about 10-5 S/m. The electronic subshell configuration, the reduced mass of unit cell, and the tolerant factor/octahedral factor related to ionic size were attempted as descriptors to classify and map out the relationship between compositions and bandgap properties of BiFeO3-based oxide perovskites. This essay paves the road for ferroelectric semiconducting oxide perovskites to make photovoltaic solar cells with power conversion efficiency promising beyond the Shockley-Queisser limit of conventional p-n junction solar cells

Study on properties of tantalum-doped La2Ti2O7 ferroelectric ceramics

A series of ceramics with a general formula, La2Ti2-xTaxO7, in which x = 0.05, 0.1, 0.2, and 0.3, were prepared by Spark Plasma Sintering (SPS). Effects of tantalum substitution for titanium on the structure, dielectric, and piezoelectric properties were studied. Results revealed that the structure changed gradually from 4-layer to 3-layer due to the higher valence of Ta. The solid solution limit of tantalum in La2Ti2O7 lattice was in the proximity of x = 0.2. The ferroelectric Curie temperature (Tc) decreased with increasing tantalum doping content. dc resistivity reached a maximum value at x = 0.2 with a value of ∼ 1.0 × 108Ω ⋅ cm at 600°C. The influence of texture on the piezoelectric properties of La2Ti2-xTaxO7 ceramics was also investigated. A maximum d33 value ∼2.1 pC/N was obtained at x = 0.2

Oxidation protective glass–ceramic coating for higher manganese silicide thermoelectrics

In this work, a silica-based glass–ceramic coating has been deposited on higher manganese silicide (HMS) thermoelectrics in order to provide oxidation protection at high temperature (up to 600 C). The coating showed good densification behaviour and an excellent thermomechanical and chemical compatibility with the HMS substrate, suppressing the silica scale formation on the HMS at high temperatures. The thermoelectric properties of the glass–ceramic-coated HMS showed excellent stability after oxidation at 600 C in air for 500 h

Oxidation protective glass-ceramic coating for higher manganese silicide thermoelectrics

In this work, a silica-based glass-ceramic coating has been deposited on higher manganese silicide (HMS) thermoelectrics in order to provide oxidation protection at high temperature (up to 600 C). The coating showed good densification behaviour and an excellent thermomechanical and chemical compatibility with the HMS substrate, suppressing the silica scale formation on the HMS at high temperatures. The thermoelectric properties of the glass-ceramic-coated HMS showed excellent stability after oxidation at 600 C in air for 500 h