Two-band conduction as a pathway to non-linear Hall effect and unsaturated negative magnetoresistance in the martensitic compound GdPd2Bi

The present work aims to address the electronic and magnetic properties of the intermetallic compound GdPd$_2$Bi through a comprehensive study of the structural, magnetic, electrical and thermal transport on a polycrystalline sample, followed by theoretical calculations. Our findings indicate that the magnetic ground state is antiferromagnetic in nature. Magnetotransport data present prominent hysteresis loop hinting a structural transition with further support from specific heat and thermopower measurements, but no such signature is observed in the magnetization study. Temperature dependent powder x-ray diffraction measurements confirm martensitic transition from the high-temperature (HT) cubic Heusler $L2_1$ structure to the low-temperature (LT) orthorhombic $Pmma$ structure similar to many previously reported shape memory alloys. The HT to LT phase transition is characterized by a sharp increase in resistivity associated with prominent thermal hysteresis. Further, we observe robust Bain distortion between cubic and orthorhombic lattice parameters related by $a_{orth} = \sqrt{2}a_{cub}$, $b_{orth} = a_{cub}$ and $c_{orth} = a_{cub}/\sqrt{2}$, that occurs by contraction along $c$-axis and elongation along $a$-axis respectively. The sample shows an unusual `non-saturating' $H^2$-dependent negative magnetoresistance for magnetic field as high as 150 kOe. In addition, non-linear field dependence of Hall resistivity is observed below about 30 K, which coincides with the sign change of the Seebeck coefficient. The electronic structure calculations confirm robust metallic states both in the LT and HT phases. It indicates complex nature of the Fermi surface along with the existence of both electron and hole charge carriers. The anomalous transport behaviors can be related to the presence of both electron and hole pockets.Comment: 13 pages, 12 figure

Impact of Copper Intercalation on Thermoelectric Properties in Polyol Method-Prepared Cu_<i>x</i>Bi₂Se₃, <i>x</i> = 0, 0.05, 0.10, and 0.15 Nanosheets

Copper-doped single-phase nanosheets (NSs) of rhombohedral CuxBi2Se3, x = 0, 0.05, 0.10, and 0.15 with the space group R3̅m of crystallite size in the range of 36–43 nm and an average thickness of 41 nm have been synthesized successfully in a modified polyol method using diethylene glycol (DEG) alone. Thermoelectric (TE) properties of these samples have been reported here. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman study show that Cu intercalates into the Bi2Se3 lattice. Notably, a large negative Seebeck coefficient with a relatively low electrical resistivity indicates their n-type semiconducting nature with low energy charge filtering in the electrical transport. A 330% enhancement in the TE figure of merit (ZT) at 300 K for x = 0.15 compared to that of x = 0 is observed due to the intercalation of Cu between quintuples and energy filtering of carriers at grain boundaries (GBs), showing a good potential of this approach. Therefore, the Cu-intercalation approach to enhance ZT has the potential to pave the way for the future development of more efficient Bi2Se3-based TE materials that can operate effectively near room temperature

Observation of intermediate bands in Eu 3+

This article explores the tuning of blue to pink colour generation from Li+ ion co-doped YPO4:5Eu nanoparticles prepared by polyol method at ∼100-120 °C with ethylene glycol (EG) as a capping agent. Interaction of EG molecules capped on the surface of the nanoparticles and/or created oxygen vacancies induces formation of intermediate/mid gap bands in the host structure, which is supported by UV-Visible absorption data. Strong blue and pink colors can be observed in the cases of as-prepared and 500 °C annealed samples, respectively. Co-doping of Li+ enhances the emission intensities of intermediate band as well as Eu3+. On annealing as-prepared sample to 500 °C, the intermediate band emission intensity decreases, whereas Eu3+ emission intensity increases suggesting increase of extent of energy transfer from the intermediate band to Eu3+ on annealing. Emission intensity ratio of electric to magnetic dipole transitions of Eu3+ can be varied by changing excitation wavelength. The X-ray photoelectron spectroscopy (XPS) study of as-prepared samples confirms the presence of oxygen vacancies and Eu3+ but absence of Eu2+. Dispersed particles in ethanol and polymer film show the strong blue color, suggesting that these materials will be useful as probes in life science and also in light emitting device applications