Thermoelectric performance of Na-doped GeSe

Recently, hole-doped GeSe materials have been predicted to exhibit extraordinary thermoelectric performance owing largely to extremely low thermal conductivity. However, experimental research on the thermoelectric properties of GeSe has received less attention. Here, we have synthesized polycrystalline Na-doped GeSe compounds, characterized their crystal structure, and measured their thermoelectric properties. The Seebeck coefficient decreases with increasing Na content up to x = 0.01 due to an increase in the hole carrier concentration and remains roughly constant at higher concentrations of Na, consistent with the electrical resistivity variation. However, the electrical resistivity is large for all samples, leading to low power factors. Powder X-ray diffraction and scanning electron microscopy/energy-dispersive spectrometry results show the presence of a ternary impurity phase within the GeSe matrix for all doped samples, which suggests that the optimal carrier concentration cannot be reached by doping with Na. Nevertheless, the lattice thermal conductivity and carrier mobility of GeSe is similar to those of polycrystalline samples of the leading thermoelectric material SnSe, leading to quality factors of comparable magnitude. This implies that GeSe shows promise as a thermoelectric material if a more suitable dopant can be found

Sn-Sb-Se crystalline phases formed by melt-quenching technique

Preperation of alloy percentages of Sn-Sb-Se(TAS) of shaking furnace and melt sealing evacuated quartz ampoule using melt quenching technique (MQT) was analyzed. XRD measurement was carried out to identify whether the prepared samples were amorphous or crystalline structure and to determine the boundary between the two states. SEM morphological studies revealed that increasing Sn and Sb mole % modify the microstructure of the ternary Sn-Sb-Se based systems. Under the same conditions of preparation and maintaining Sn mol% at 15, the dendrite shapes of crystals were enlarged when Sb mol% increased. The Sn occurred in ternary compositions and supports the theoretical argument which considered Sb-mol %=14.3 is the boundary line between the crystalline and crystalline phase is dominant in the region with Sb-mol% more than or equal to 15. MQT proved its ability in preparing alloy of Sn-Sb-Se in crystalline structure and there was no excessive loss of the materials during the preparation

Relief grating induced by photo-expansion in Ga-Ge-S and Ga-Ge-As-S glasses

We report the fabrication of relief diffraction gratings recorded on a surface of photosensitive Ga10Ge25S65 and Ga5Ge25As5S65 glasses by means of interference of two UV laser beams at 351 nm. The diffraction efficiency (eta) of first diffraction order was measured. Atomic-force-microscope (AFM) was used to perform a 3D imaging analysis of the sample surface topography that shows the superposition of an imprinted grating over the topography of the glass. The change in the absorption edge and the refractive index has been evaluated and a structural approach of the relief grating on the glass surface has been discussed.Univ São Paulo, Inst Fis, BR-13560970 Sao Carlos, SP, BrazilASCR, Lab Inorgan Mat IIC ASCR, Prague 6, Czech RepublicICT, Prague 6, Czech RepublicUNESP, Inst Quim, BR-14801970 Araraquara, SP, BrazilUNESP, Inst Quim, BR-14801970 Araraquara, SP, Brazi

Relief grating induced by photo-expansion in Ga-Ge-S and Ga-Ge-As-S glasses

We report the fabrication of relief diffraction gratings recorded on a surface of photosensitive Ga10Ge25S65 and Ga5Ge25As5S65 glasses by means of interference of two UV laser beams at 351 nm. The diffraction efficiency (eta) of first diffraction order was measured. Atomic-force-microscope (AFM) was used to perform a 3D imaging analysis of the sample surface topography that shows the superposition of an imprinted grating over the topography of the glass. The change in the absorption edge and the refractive index has been evaluated and a structural approach of the relief grating on the glass surface has been discussed

Relief grating induced by photo-expansion in Ga-Ge-S and Ga-Ge-As-S glasses

We report the fabrication of relief diffraction gratings recorded on a surface of photosensitive Ga10Ge25S65 and Ga5Ge25As5S65 glasses by means of interference of two UV laser beams at 351 nm. The diffraction efficiency (η) of first diffraction order was measured. Atomic-force-microscope (AFM) was used to perform a 3D imaging analysis of the sample surface topography that shows the superposition of an imprinted grating over the topography of the glass. The change in the absorption edge and the refractive index has been evaluated and a structural approach of the relief grating on the glass surface has been discussed.Instituto de Física de São Carlos Universidade de São Paulo, C.P. 369, CEP: 13560-970, São Carlos, SPLaboratory of Inorganic Materials IIC ASCR and ICT, Pelleova 24, Prague 6Instituto de Química UNESP - Araraquara, C.P. 355, CEP: 14801-970, Araraquara, SPInstituto de Química UNESP - Araraquara, C.P. 355, CEP: 14801-970, Araraquara, S