Copper and silver based chalcogenides, chalco-halides, and halides form a unique class of semiconductors, as they display mixed ionic and electronic conduction in their superionic phase. These ...compounds are composed of softly coupled cationic and anionic substructures, and undergo a transition to a superionic phase displaying changes in the substructure of their mobile ions with varying temperature. Here, we demonstrate a facile, ambient and capping agent free solution based synthesis of AgCuS nanocrystals and their temperature dependent (300-550 K) thermoelectric properties. AgCuS is known to show fascinating p-n-p type conduction switching in its bulk polycrystalline form. Temperature dependent synchrotron powder X-ray diffraction, heat capacity and Raman spectroscopy measurements indicate the observation of two superionic phase transitions, from a room temperature ordered orthorhombic (β) to a partially disordered hexagonal (α) phase at ∼365 K and from the hexagonal (α) to a fully disordered cubic (δ) phase at ∼439 K, in nanocrystalline AgCuS. The size reduction to the nanoscale resulted in a large variation in the thermoelectric properties compared to its bulk counterpart. Temperature dependent Seebeck coefficient measurements indicate that the nanocrystalline AgCuS does not display the p-n-p type conduction switching property like its bulk form, but remains p-type throughout the measured temperature range due to the presence of excess localized Ag vacancies. Nanocrystalline AgCuS exhibits a wider electronic band gap (∼1.2 eV) compared to that of the bulk AgCuS (∼0.9 eV), which is not sufficient to close the band gap to form a semimetallic intermediate state during the orthorhombic to hexagonal superionic phase transition, thus AgCuS nanocrystals do not show conduction type switching properties like their bulk counterpart. The present study demonstrates that ambient solution phase synthesis and size reduction to the nanoscale can tailor the order-disorder phase transition, the band gap and the electronic conduction properties in superionic compounds, which will not only enrich solid-state inorganic chemistry but also open a new avenue to design multifunctional materials.
Crystalline solids with intrinsically low lattice thermal conductivity (κL) are crucial to realizing high‐performance thermoelectric (TE) materials. Herein, we show an ultralow κL of 0.35 Wm−1 K−1 in ...AgCuTe, which has a remarkable TE figure‐of‐merit, zT of 1.6 at 670 K when alloyed with 10 mol % Se. First‐principles DFT calculation reveals several soft phonon modes in its room‐temperature hexagonal phase, which are also evident from low‐temperature heat‐capacity measurement. These phonon modes, dominated by Ag vibrations, soften further with temperature giving a dynamic cation disorder and driving the superionic transition. Intrinsic factors cause an ultralow κL in the room‐temperature hexagonal phase, while the dynamic disorder of Ag/Cu cations leads to reduced phonon frequencies and mean free paths in the high‐temperature rocksalt phase. Despite the cation disorder at elevated temperatures, the crystalline conduits of the rigid anion sublattice give a high power factor.
Low thermal conduction: Soft phonon modes and optical‐acoustic phonon coupling cause an ultralow lattice thermal conductivity in the room‐temperature hexagonal phase of AgCuTe, while the dynamic disorder of Ag/Cu cations leads to reduced phonon frequencies and mean free paths in the high‐temperature rocksalt phase. A high thermoelectric figure of merit (zT) of 1.6 is achieved in the p‐type AgCuTe at around 670 K.
P-type conductivity in MOCVD grown ZnO was obtained by directional thermal diffusion of arsenic from semi-insulating GaAs substrate. The films were single crystalline in nature and oriented along ...(002) direction. Ab initio calculations in the framework of density functional theory have been carried out with different chemical states of arsenic in ZnO. Present calculations suggested AsZn–2VZn defect is a shallow acceptor and results in ferromagnetism in ZnO. The magnetic measurements of the samples indeed showed ferromagnetic ordering at room temperature. X-ray photoelectron spectra confirmed the presence of AsZn and VZn. The core level chemical shift in binding energy of AsZn indicated the formation of AsZn–2VZn. Diffused arsenic substitutes zinc atom and creates additional zinc vacancies. The zinc vacancies, surrounding the oxygen atoms, result in unpaired O 2p electrons which in turn induce ferromagnetism in the samples.
•Single crystalline ZnO films were grown onto semi-insulating GaAs substrate by MOCVD.•Directional thermal diffusion of As from GaAs gave rise p-type conductivity in ZnO.•DFT calculations revealed p-type nature along with ferromagnetism by AsZn–2VZn state.•Magnetic measurements established ferromagnetism nature of the films after As doping.•X-ray photoelectron spectra indicated the presence of AsZn–2VZn acceptor states.
Magnetic properties of 3d transition metal ion doped methylammonium lead chloride (MAPbCl
3
) have been studied by ab-initio calculations in the framework of density functional theory. The study of ...spin-spin interactions reveals that doping (about 2%) of Ti, V, Cr, Mn and Fe at the Pb site of MAPbCl
3
shows stable ferromagnetic ordering along with the half-metallic behaviour. 3d orbital electrons of the dopants are primarily responsible for the origin of the magnetic moment and the remaining part comes from the p-d exchange interaction between the 3d orbital electrons of the dopants and the 6p orbital electrons of Pb in the vicinity of the doping position. Additionally, the band structure calculations suggest that the doped system shows n/p-type semiconducting behaviour. Ferromagnetism, along with semiconducting behaviour in transition metal ion-doped MAPbCl
3,
will be suitable for spintronic applications.
•High magnetic moment has been observed in Mo doped methylammonium lead halide.•The generated moment favors ferromagnetic ordering.•The d-orbital electrons of the doped Mo are the primary source of ...magnetic moment.
Magnetic properties of molybdenum doped methylammonium lead halides (MAPbX3, X = Cl, Br, I) system has been studied using density functional theory for the very first time. Spin-polarized magnetic calculations indicate that the doping of Mo-atoms at Pb-site generates a significant magnetic moment in all the three MAPbX3 systems, where the d-orbital electrons of the dopant primarily generate the induced magnetism in the system. The Spin density distribution and Bader charge analysis also support that the magnetic moment is concentrated around the dopant. The unpaired spins of the Mo-dopants prefer parallel alignment, which makes a stable ferromagnetic spin ordered system. The defect formation energy of the Mo-doping at Pb-site is also small, which makes it a potential candidate for spintronics application.
A two‐step optimization strategy is used to improve the thermoelectric performance of SnTe via modulating the electronic structure and phonon transport. The electrical transport of self‐compensated ...SnTe (that is, Sn1.03Te) was first optimized by Ag doping, which resulted in an optimized carrier concentration. Subsequently, Mn doping in Sn1.03−xAgxTe resulted in highly converged valence bands, which improved the Seebeck coefficient. The energy gap between the light and heavy hole bands, i.e. ΔEv decreases to 0.10 eV in Sn0.83Ag0.03Mn0.17Te compared to the value of 0.35 eV in pristine SnTe. As a result, a high power factor of ca. 24.8 μW cm−1 K−2 at 816 K in Sn0.83Ag0.03Mn0.17Te was attained. The lattice thermal conductivity of Sn0.83Ag0.03Mn0.17Te reached to an ultralow value (ca. 0.3 W m−1 K−1) at 865 K, owing to the formation of Ag7Te4 nanoprecipitates in SnTe matrix. A high thermoelectric figure of merit (z T≈1.45 at 865 K) was obtained in Sn0.83Ag0.03Mn0.17Te.
The thermoelectric four: Highly converged valence bands and ultralow lattice thermal conductivity owing to nanoprecipitates lead to a high thermoelectric figure of merit (z T≈1.45 at 865 K) in Sn0.83Ag0.03Mn0.17Te, which is higher than that of Ag alone or Mn‐doped SnTe.
Ferromagnetic properties in titanium doped methyl ammonium lead halides (MAPbX3, X = I, Cl, Br) have been analyzed using first principles calculations in the framework of density functional theory. ...Titanium doped at the Pb site of methyl ammonium lead halides shows n-type semiconducting property along with a significant amount of magnetic moment. The total and partial density of state calculations reveals that d orbital of Ti atom is the main source of magnetism and a small contribution comes from the p orbital of Pb and halide ions. The calculated value of low defect formation energy makes it a suitable material for spintronics applications. Bader charge analysis and band structure calculations have been performed for the pristine and doped systems.
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•CoFe2-xBixO4 (x = 0, 0.05, 0.1, 0.5, 1.0) nanoparticles were prepared and gamma irradiated.•Reduction in lattice constant and particle size is seen as the consequences of gamma ...irradiation.•The grain size was reported in the range of 37–17 nm after gamma irradiation.•Radiation induces changes in electrical and magnetic properties.•Ms, Mr and Hc were reported to be reduced after gamma irradiation.
The effects of gamma irradiation on the structural, dielectric, magnetic and ferroelectric behaviour of Bi doped cobalt ferrite, CoFe2-xBixO4 (x = 0, 0.05, 0.1, 0.5, 1.0) synthesized by glycine nitrate method before and after gamma irradiation have been investigated. A micro-strain is generated by the gamma irradiation as observed by the X-ray diffraction studies. The massive enhancement of dielectric constant in irradiated samples is attributed to the Maxwell–Wagner type of interfacial polarization. Complex impedance analysis indicates a predominant grain boundary contribution to the conduction mechanism. The frequency-dependent ac conductivity in the frequency range of 100 Hz – 1 MHz is increased on irradiation. Reduction in magnetisation was found in the irradiated samples. Remnant polarization and coercive field decreases with irradiation as obtained from P-E loop. Hence, the applications of these nanoferrites in the field of high frequency and magnetic recording devices can be favoured by tailoring the electrical and magnetic properties subjected to gamma irradiation.
The effect of the substitutional and vacancy type defects on the H
2
adsorption energy over a monolayer hexagonal boron nitride (h-BN) substrate has been studied by using the van der Waals density ...functional theory calculations. Carbon doping at the boron site or formation of boron vacancy can be an effective way to increase the adsorption energy value of a pristine h-BN substrate. The repulsive lateral interaction present in between the two H
2
molecules plays a vital role in case of multiple H
2
molecule adsorption over the substrate. Also, the carbon cluster formation during doping can have a favorable effect in the overall storage capacity of the h-BN substrate.
Dilute magnetic semiconductor (DMS) is a trending research topic in material science for its requirements in spintronics technology in recent times. The present work reports the electrical and ...magnetic properties of different transition metal ions (Ti, V, Cr, Mn, Fe, Co, Ni and Zn)- doped silver copper sulphide. The dilute doping of transition metal ions at the copper site induces significant magnetic moments, which ordered ferromagnetically. The 3d orbital of the transition metal ions and the d orbital of Cu and Ag ions are the source of magnetisation.
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