A new compound Ce_(2)PtGe_(3) was synthesized using arc-melting process.The compound crystallizes in an orthorhombic Cmce crystal structure with lattice parameters a=8.5157(17)Å,b=14.7496(29)Å and c=4.2511(9...A new compound Ce_(2)PtGe_(3) was synthesized using arc-melting process.The compound crystallizes in an orthorhombic Cmce crystal structure with lattice parameters a=8.5157(17)Å,b=14.7496(29)Å and c=4.2511(9)Å.The structure of Ce_(2)PtGe_(3) can be derived from the structure of YAlGe,which is another superstructure derivative of the AlB_(2) prototype crystallizing in the Cmcm space group.The crystal structure of Ce_(2)PtGe_(3) is composed of infinite arrays of hexagonal[Pt_(3)Ge_(3)]units stacked along the b-axis and the Ce sites are sandwiched between these parallel hexagonal networks,which is closely related to the other known orthorhombic superstructures Ca_(2)AgSi_(3)(SG:Fmmm)and Ba_(2)LiSi_(3)(SG:Fddd)in the AlB_(2) family.Both DC and AC susceptibility measurements reveal a spin glass state probably arising from nonmagnetic atomic disorder(NMAD)from positional disorder from a part of Pt and Ge crystallographic sites.This was further supported by specific heat capacity measurements with a high value of γ=125 mJ mol^(-1) K^(-2).The modified Curie-Weiss fitting yielded a residual magnetic moment(χ_(0))0.0011 emu mol^(-1),and Curie paramagnetic temperature,θ_(p)=^(-2)1.5 K suggesting antiferromagnetic coupling and an effective magnetic moment of 3.09μB per Ce which indicates the presence of Ce^(3+).A thorough analysis of the temperature dependent resistivity data revealed that the compound might be a Kondo semiconductor at low temperature.展开更多
The expression ofβ-lactamase,particularly metallo-β-lactamase(MBL)in bacteria has caused significant resistance to clinically importantβ-lactam antibiotics,including life-saving carbapenems.Antimicrobial peptides(A...The expression ofβ-lactamase,particularly metallo-β-lactamase(MBL)in bacteria has caused significant resistance to clinically importantβ-lactam antibiotics,including life-saving carbapenems.Antimicrobial peptides(AMPs)have emerged as promising therapeutic agents to combat antibiotic resistance.However,the cytotoxic AMPs has been one of the major concerns for their applications in clinical practice.Herein,we report a novel cephalosporin-caged AMP,which shows significantly reduced cytotoxicity,hemolytic activity,and antibacterial activity but turns highly active against bacteria upon specific hydrolysis by the antimicrobial resistance-causativeβ-lactamase.Further investigations demonstrate thisβ-lactamaseactivatable AMP selectively inactivates resistant bacterial pathogens over susceptible bacteria.This strategy should be applicable to other AMPs as a potential solution for the treatment of infectious diseases caused byβ-lactamase-expressing pathogenic bacteria.展开更多
The high quality single crystals of Yb5Co4Ge10 have been grown by the indium metal flux method and characterized by means of single crystal X-ray diffraction data. Yb5Co4Ge10 crystallizes in the Sc5Co4Si10 structure t...The high quality single crystals of Yb5Co4Ge10 have been grown by the indium metal flux method and characterized by means of single crystal X-ray diffraction data. Yb5Co4Ge10 crystallizes in the Sc5Co4Si10 structure type, tetragonal space group P4/mbm and lattice constants are a = b = 12.6369(18) ? and c = 4.1378(8) ?. Crystal structure of Yb5Co4Ge10 composed of three-dimensional [Co4Ge12] network having five, six and eight membered rings. The three non-equivalent Yb atoms are sandwiched in three different channels created by the [Co4Ge12] network. Based on the bond length analysis from the crystallographic information, we confirmed that Yb1 and Yb2 atoms are in the trivalent magnetic state and Yb3 is in the divalent non-magnetic state.展开更多
A promising thermoelectric figure of merit,zT,of~1.3 at 725 K was obtained in high quality crystalline ingots of Ge_(1−x)Bi_(x)Te.The substitution of Bi^(3+)in a Ge^(2+)sublattice of GeTe significantly reduces the exc...A promising thermoelectric figure of merit,zT,of~1.3 at 725 K was obtained in high quality crystalline ingots of Ge_(1−x)Bi_(x)Te.The substitution of Bi^(3+)in a Ge^(2+)sublattice of GeTe significantly reduces the excess hole concentration due to the aliovalent donor dopant nature of Bi^(3+).Reduction in carrier density optimizes electrical conductivity,and subsequently enhances the Seebeck coefficient in Ge_(1−x)Bi_(x)Te.More importantly,a low lattice thermal conductivity of~1.1 W m^(−1) K^(−1) for Ge_(0.90)Bi_(0.10)Te was achieved,which is due to the collective phonon scattering from meso-structured grain boundaries,nano-structured precipitates,nano-scale defect layers,and solid solution point defects.We have obtained a reasonably high mechanical stability for the Ge_(1−x)Bi_(x)Te samples.The measured Vickers microhardness value of the high performance sample is∼165 HV,which is comparatively higher than that of state-of-the-art thermoelectric materials,such as PbTe,Bi_(2)Te_(3),and Cu_(2)Se.展开更多
Layered materials with intrinsically low thermal conductivity are promising candidates for thermoelectric waste heat to electrical energy conversion.Recently bulk form BiCuSeO,a layered oxychalcogenide,has drawn atten...Layered materials with intrinsically low thermal conductivity are promising candidates for thermoelectric waste heat to electrical energy conversion.Recently bulk form BiCuSeO,a layered oxychalcogenide,has drawn attention for thermoelectric applications.However,synthesis of a two dimensional nanosheet of BiCuSeO and study of its thermoelectric properties have not been explored yet.Here,we present a facile surfactant free low temperature solvothermal synthesis of few layered ultrathin BiCuSeO nanosheets for the first time.Nanosheets of BiCuSeO exhibit a semiconducting band gap of 0.9 eV and p-type conduction.A dense hot pressed pellet of BiCuSeO nanosheets exhibits a superior power factor and lower lattice thermal conductivity compared to that of the bulk sample in the temperature range of 300-723 K.展开更多
The most essential prerequisite for the hydrogen economy is sustainable hydrogen production.The electrochemical hydrogen evolution reaction is a well-studied electrochemical reaction which involves the reduction of pr...The most essential prerequisite for the hydrogen economy is sustainable hydrogen production.The electrochemical hydrogen evolution reaction is a well-studied electrochemical reaction which involves the reduction of protons for hydrogen production.It requires highly efficient and robust catalysts to lower the overpotential and energy consumption.Platinum(Pt)remains the first choice among electrocatalysts because of its excellent activity and high current density.Since Pt is limited by its high cost and scarcity,extensive research is devoted for the development of non-Pt-based cost-effective electrocatalysts.According to the volcano plot,palladium(Pd)can be used as a substitute for Pt towards the hydrogen evolution reaction(HER).Herein,we review various Pd-based electrocatalysts in the form of nanoparticles,alloys,bimetallics and intermetallics reported for the HER.In this review we have emphasized various synthesis techniques employed for these electrocatalysts and the strategies used for improving the catalytic performance.We conclude with a perspective on the future aspects of electrocatalysts based on Pd.展开更多
Five new coordination polymers,{[Cu(H_(2)iso)_(2)]·2H_(2)O}_(n)(1),{Mn(Hiso)(H_(2)O)_(3)}_(n)(2),{Mn(Hiso)(H_(2)O)_(2)}_(n)(3),{[Cu(Hiso)(4,4’-bipy)(H_(2)O)]·2H_(2)O}_(n)(4)and{[Ni(Hiso)(4,4’-bipy)(H_(2)O)...Five new coordination polymers,{[Cu(H_(2)iso)_(2)]·2H_(2)O}_(n)(1),{Mn(Hiso)(H_(2)O)_(3)}_(n)(2),{Mn(Hiso)(H_(2)O)_(2)}_(n)(3),{[Cu(Hiso)(4,4’-bipy)(H_(2)O)]·2H_(2)O}_(n)(4)and{[Ni(Hiso)(4,4’-bipy)(H_(2)O)]·0.5(4,4’-bipy)}_(n)(5)(H_(3)iso=2,4-dihydroxypyrimidine-5-carboxylic acid or isoorotic acid;4,4’-bipy=4,4’-bipyridyl),have been synthesized using hydrothermal as well as room temperature solvent diffusion techniques and structurally characterized.Compounds 1 and 2 are 1D coordination polymers which are further connected by O–H⋯N,O–H⋯O hydrogen bonding interactions forming 3D supramolecular frameworks.Compound 3 is a 2D coordination polymer where 1D chains of{Mn(Hiso)(H_(2)O)_(2)}are linked by an oxo(μ_(2)-O)bridge.Compound 4 consists of isoorotic acid and 4,4’-bipy,a mixed linker system.It forms a 2D sheet like extended structure and these sheets stack on each other to give a 3D supramolecular porous structure.In case of 5,Ni(Hiso)1D chains are bridged by 4,4’-bipy forming a 2D network and networks are further interdigitated through hydrogen bonding interactions resulting in a 3D supramolecular framework with a 1D channel where 4,4’-bipy molecules are accommodated as vips.Compound 5 undergoes a structural contraction after the removal of the vip 4,4’-bipy and metal bound water molecules and shows a non-porous behaviour toward N_(2) at 77 K.However,at 195 K,it shows a stepwise uptake for both CO_(2) and C_(2)H_(2),suggesting the flexible nature and polar pore surface of the framework.展开更多
Correction for‘1D chains,2D networks and 3D interdigitated frameworks of isoorotic acid or 4,4’-bipyridyl and isoorotic acid:syntheses,structures,and sorption properties’by Ritesh Haldar et al.,Inorg.Chem.Front.,20...Correction for‘1D chains,2D networks and 3D interdigitated frameworks of isoorotic acid or 4,4’-bipyridyl and isoorotic acid:syntheses,structures,and sorption properties’by Ritesh Haldar et al.,Inorg.Chem.Front.,2015,2,278-289.展开更多
In this work,we have studied the structure and physical properties of a series of intermetallic compounds with the general formula CePd_(x)Ge_(2−x)(where,x=0.21,0.32,0.69).It was found that the compound crystallizes i...In this work,we have studied the structure and physical properties of a series of intermetallic compounds with the general formula CePd_(x)Ge_(2−x)(where,x=0.21,0.32,0.69).It was found that the compound crystallizes in three different phases with stoichiometries:CePd_(0.32)Ge_(1.68),CePd_(0.21)Ge_(1.79) and CePd_(0.69)Ge_(1.31) by varying the Pd to Ge ratio.While CePd_(0.32)Ge_(1.68) and CePd_(0.69)Ge_(1.31) crystallize in the hexagonal AlB2 structure type with the space group P6/mmm,CePd_(0.21)Ge_(1.79) crystallizes in the tetragonalα-ThSi_(2) structure type with the space group I41/amd.CePd_(0.69)Ge_(1.31) is in fact an ordered superstructure of CePd_(0.32)Ge_(1.68) with tripling of the c-lattice.Relative changes in the Pd/Ge ratio also impart substantial variation in their magnetic properties,although Ce is in the trivalent state in both the phases.CePd_(0.21)Ge_(1.79) shows metamagnetic behavior below 10 K whereas CePd_(0.69)Ge_(1.31) showed ferromagnetic behavior in the same temperature range.In addition to the metamagnetic behavior,CePd_(0.21)Ge_(1.79) also shows spin glass behavior at low temperature.DFT calculations were used to obtain ulterior information on the CePd_(0.69)Ge_(1.31) phase.Self-consistent calculations revealed that the ferromagnetic ordering of the ground state arises from the spins at the Ce and Pd sites.The observed sharp rise in the low temperature resistivity of CePd_(0.69)Ge_(1.31) is an indication of a pseudo-gap formation or possible Kondo behavior in the electronic density of states,enhancing the scattering of the charge carriers.Heat capacity measurements on CePd_(0.69)Ge_(1.31) suggest that it falls in the category of medium heavy fermion compounds.展开更多
CONSPECTUS:There is an extensive history of research on both inorganic and hybrid metal halides,with the latter being first reported in the 1960s.Although work on hybrid systems has progressed steadily over the last 6...CONSPECTUS:There is an extensive history of research on both inorganic and hybrid metal halides,with the latter being first reported in the 1960s.Although work on hybrid systems has progressed steadily over the last 60 years,it has enjoyed a major renaissance during the last 5 years.This has arisen as a consequence of the 2009 discovery of the outstanding optoelectronic properties of hybrid lead halides,such as(MA)PbI_(3)(MA=methylammonium),and the recognition that there are many opportunities for equally exciting discoveries with compounds of the transition metals.Some of the early work on hybrid transition-metal halides put more emphasis on crystal structures but less on properties.In the modern era,we aim to grasp both the structure and properties,with a new twist.In this Account,we shall explore the recent developments in hybrid transition-metal halides with a focus on work in four main areas:magnetism,photoluminescence,semiconductivity,and spintronics.Our work on magnetism centers on the Ru-based hybrid halides,where the structural types are diversely composed of vacancy-ordered double perovskite,as well as chain-like one-dimensional structures and layered double perovskite(LDP)when paired with a(1+)metal.We explore their magnetic properties and find that their spin−orbit coupling(SOC)behavior can be tuned through changing the A cation and the halide.In the luminescence section,we focus on our recent works on hybrid tetrahedral Mn(II)bromides and Cu(I)and Ag(I)iodides.We correlated our newly discovered 0D A_(m)MnBr_(4)(A=organic cation,m=1 or 2)compounds with previous reports,and generated a trend where the photoluminescence quantum yield(PLQY)increases with larger Mn−Mn distances.The flexible organic cation becomes the most important tool here to tune the structure−PLQY relations.Cu(I)and Ag(I)iodides coordinated with iodides and organic ligands produce new crystal structures with intense PL.For the semiconducting properties,we explore the Pt-based vacancy-ordered double perovskite and hybrid bismuth and indium-based LDPs to show the structural evolution with different choices for the organic cation,the metal and the halide;these have a strong influence on the optical properties.The LDPs specifically exhibit high structure tunability,with a wide range of(1+)and(3+)metal choices,and are exempt from some of the limitations of 3D double perovskite.In the last section,we introduce the recent progress on hybrid transition-metal-based ferroelectrics and spintronic materials.We successfully demonstrate the utilization of chiral Cu(II)chlorides for circularly polarized light(CPL)detection,showing the high anisotropy of the photoresponsivity.We also highlight the work that the authors have contributed in these areas and suggest several exciting opportunities for future developments.展开更多
Sustainable thermoelectric materials open an avenue of emission-free as well as fast-responding recycling of energy in terms of heat to electricity.The efficiency(η)of such conversion is primarily guided by the dimen...Sustainable thermoelectric materials open an avenue of emission-free as well as fast-responding recycling of energy in terms of heat to electricity.The efficiency(η)of such conversion is primarily guided by the dimensionless thermoelectric figure of merit(zT),which depends on parameters like Seebeck coefficient(S).展开更多
基金the Jawaharlal Nehru Centre for Advanced Scientific Research,Sheikh Saqr Laboratory and Department of Science and Technology,India(DST),Council of Scientific and Industrial Research(CSIR)(01(2787)/14/EMR-Ⅱ)for financial supportthe CSIR for a research fellowship+1 种基金a UGC fellowshipthe UGC-DAE CSR,Mumbai center for a project fellowship(Project No.CRS-M-166).
文摘A new compound Ce_(2)PtGe_(3) was synthesized using arc-melting process.The compound crystallizes in an orthorhombic Cmce crystal structure with lattice parameters a=8.5157(17)Å,b=14.7496(29)Å and c=4.2511(9)Å.The structure of Ce_(2)PtGe_(3) can be derived from the structure of YAlGe,which is another superstructure derivative of the AlB_(2) prototype crystallizing in the Cmcm space group.The crystal structure of Ce_(2)PtGe_(3) is composed of infinite arrays of hexagonal[Pt_(3)Ge_(3)]units stacked along the b-axis and the Ce sites are sandwiched between these parallel hexagonal networks,which is closely related to the other known orthorhombic superstructures Ca_(2)AgSi_(3)(SG:Fmmm)and Ba_(2)LiSi_(3)(SG:Fddd)in the AlB_(2) family.Both DC and AC susceptibility measurements reveal a spin glass state probably arising from nonmagnetic atomic disorder(NMAD)from positional disorder from a part of Pt and Ge crystallographic sites.This was further supported by specific heat capacity measurements with a high value of γ=125 mJ mol^(-1) K^(-2).The modified Curie-Weiss fitting yielded a residual magnetic moment(χ_(0))0.0011 emu mol^(-1),and Curie paramagnetic temperature,θ_(p)=^(-2)1.5 K suggesting antiferromagnetic coupling and an effective magnetic moment of 3.09μB per Ce which indicates the presence of Ce^(3+).A thorough analysis of the temperature dependent resistivity data revealed that the compound might be a Kondo semiconductor at low temperature.
基金financial support from the NSFC-BRICS(No.81861148020,H.Xie)the Fundamental Research Funds for the Central Universities(H.Xie)+1 种基金the Research Program of State Key Laboratory of Bioreactor Engineering(H.Xie)DST-BRICS multilateral cooperation project(DST/IMRCD/BRICS/PilotCall2/MBLI/2018(G))。
文摘The expression ofβ-lactamase,particularly metallo-β-lactamase(MBL)in bacteria has caused significant resistance to clinically importantβ-lactam antibiotics,including life-saving carbapenems.Antimicrobial peptides(AMPs)have emerged as promising therapeutic agents to combat antibiotic resistance.However,the cytotoxic AMPs has been one of the major concerns for their applications in clinical practice.Herein,we report a novel cephalosporin-caged AMP,which shows significantly reduced cytotoxicity,hemolytic activity,and antibacterial activity but turns highly active against bacteria upon specific hydrolysis by the antimicrobial resistance-causativeβ-lactamase.Further investigations demonstrate thisβ-lactamaseactivatable AMP selectively inactivates resistant bacterial pathogens over susceptible bacteria.This strategy should be applicable to other AMPs as a potential solution for the treatment of infectious diseases caused byβ-lactamase-expressing pathogenic bacteria.
文摘The high quality single crystals of Yb5Co4Ge10 have been grown by the indium metal flux method and characterized by means of single crystal X-ray diffraction data. Yb5Co4Ge10 crystallizes in the Sc5Co4Si10 structure type, tetragonal space group P4/mbm and lattice constants are a = b = 12.6369(18) ? and c = 4.1378(8) ?. Crystal structure of Yb5Co4Ge10 composed of three-dimensional [Co4Ge12] network having five, six and eight membered rings. The three non-equivalent Yb atoms are sandwiched in three different channels created by the [Co4Ge12] network. Based on the bond length analysis from the crystallographic information, we confirmed that Yb1 and Yb2 atoms are in the trivalent magnetic state and Yb3 is in the divalent non-magnetic state.
基金partially supported by the DRDO-JNCASR collaborative project and DAE-BRNS project(37(3)20/01/2015/BRNS)support of the DST Ramanujan Fellowship and Sheikh Saqr Laboratory.
文摘A promising thermoelectric figure of merit,zT,of~1.3 at 725 K was obtained in high quality crystalline ingots of Ge_(1−x)Bi_(x)Te.The substitution of Bi^(3+)in a Ge^(2+)sublattice of GeTe significantly reduces the excess hole concentration due to the aliovalent donor dopant nature of Bi^(3+).Reduction in carrier density optimizes electrical conductivity,and subsequently enhances the Seebeck coefficient in Ge_(1−x)Bi_(x)Te.More importantly,a low lattice thermal conductivity of~1.1 W m^(−1) K^(−1) for Ge_(0.90)Bi_(0.10)Te was achieved,which is due to the collective phonon scattering from meso-structured grain boundaries,nano-structured precipitates,nano-scale defect layers,and solid solution point defects.We have obtained a reasonably high mechanical stability for the Ge_(1−x)Bi_(x)Te samples.The measured Vickers microhardness value of the high performance sample is∼165 HV,which is comparatively higher than that of state-of-the-art thermoelectric materials,such as PbTe,Bi_(2)Te_(3),and Cu_(2)Se.
基金supported by SERB,DST(EMR/2016/000651)the New Chemistry Unit and the Sheikh Saqr Laboratory.
文摘Layered materials with intrinsically low thermal conductivity are promising candidates for thermoelectric waste heat to electrical energy conversion.Recently bulk form BiCuSeO,a layered oxychalcogenide,has drawn attention for thermoelectric applications.However,synthesis of a two dimensional nanosheet of BiCuSeO and study of its thermoelectric properties have not been explored yet.Here,we present a facile surfactant free low temperature solvothermal synthesis of few layered ultrathin BiCuSeO nanosheets for the first time.Nanosheets of BiCuSeO exhibit a semiconducting band gap of 0.9 eV and p-type conduction.A dense hot pressed pellet of BiCuSeO nanosheets exhibits a superior power factor and lower lattice thermal conductivity compared to that of the bulk sample in the temperature range of 300-723 K.
文摘The most essential prerequisite for the hydrogen economy is sustainable hydrogen production.The electrochemical hydrogen evolution reaction is a well-studied electrochemical reaction which involves the reduction of protons for hydrogen production.It requires highly efficient and robust catalysts to lower the overpotential and energy consumption.Platinum(Pt)remains the first choice among electrocatalysts because of its excellent activity and high current density.Since Pt is limited by its high cost and scarcity,extensive research is devoted for the development of non-Pt-based cost-effective electrocatalysts.According to the volcano plot,palladium(Pd)can be used as a substitute for Pt towards the hydrogen evolution reaction(HER).Herein,we review various Pd-based electrocatalysts in the form of nanoparticles,alloys,bimetallics and intermetallics reported for the HER.In this review we have emphasized various synthesis techniques employed for these electrocatalysts and the strategies used for improving the catalytic performance.We conclude with a perspective on the future aspects of electrocatalysts based on Pd.
文摘Five new coordination polymers,{[Cu(H_(2)iso)_(2)]·2H_(2)O}_(n)(1),{Mn(Hiso)(H_(2)O)_(3)}_(n)(2),{Mn(Hiso)(H_(2)O)_(2)}_(n)(3),{[Cu(Hiso)(4,4’-bipy)(H_(2)O)]·2H_(2)O}_(n)(4)and{[Ni(Hiso)(4,4’-bipy)(H_(2)O)]·0.5(4,4’-bipy)}_(n)(5)(H_(3)iso=2,4-dihydroxypyrimidine-5-carboxylic acid or isoorotic acid;4,4’-bipy=4,4’-bipyridyl),have been synthesized using hydrothermal as well as room temperature solvent diffusion techniques and structurally characterized.Compounds 1 and 2 are 1D coordination polymers which are further connected by O–H⋯N,O–H⋯O hydrogen bonding interactions forming 3D supramolecular frameworks.Compound 3 is a 2D coordination polymer where 1D chains of{Mn(Hiso)(H_(2)O)_(2)}are linked by an oxo(μ_(2)-O)bridge.Compound 4 consists of isoorotic acid and 4,4’-bipy,a mixed linker system.It forms a 2D sheet like extended structure and these sheets stack on each other to give a 3D supramolecular porous structure.In case of 5,Ni(Hiso)1D chains are bridged by 4,4’-bipy forming a 2D network and networks are further interdigitated through hydrogen bonding interactions resulting in a 3D supramolecular framework with a 1D channel where 4,4’-bipy molecules are accommodated as vips.Compound 5 undergoes a structural contraction after the removal of the vip 4,4’-bipy and metal bound water molecules and shows a non-porous behaviour toward N_(2) at 77 K.However,at 195 K,it shows a stepwise uptake for both CO_(2) and C_(2)H_(2),suggesting the flexible nature and polar pore surface of the framework.
文摘Correction for‘1D chains,2D networks and 3D interdigitated frameworks of isoorotic acid or 4,4’-bipyridyl and isoorotic acid:syntheses,structures,and sorption properties’by Ritesh Haldar et al.,Inorg.Chem.Front.,2015,2,278-289.
基金We thank the Jawaharlal Nehru Centre for Advanced Scientific Research,Sheikh Saqr Laboratory and Department of Science and Technology,India(DST),and the Council of Scientific and Industrial Research(CSIR)(01(2787)/14/EMR-II)for financial supportS.S thanks the CSIR for research fellowship,D.K.and P.H.thank the UGC-DAE CSR,Mumbai center for project fellowship(Project No.CRS-M-166)S.C.P thanks the DST for the Ramanujan fellowship(Grant SR/S2/RJN-24/2010).
文摘In this work,we have studied the structure and physical properties of a series of intermetallic compounds with the general formula CePd_(x)Ge_(2−x)(where,x=0.21,0.32,0.69).It was found that the compound crystallizes in three different phases with stoichiometries:CePd_(0.32)Ge_(1.68),CePd_(0.21)Ge_(1.79) and CePd_(0.69)Ge_(1.31) by varying the Pd to Ge ratio.While CePd_(0.32)Ge_(1.68) and CePd_(0.69)Ge_(1.31) crystallize in the hexagonal AlB2 structure type with the space group P6/mmm,CePd_(0.21)Ge_(1.79) crystallizes in the tetragonalα-ThSi_(2) structure type with the space group I41/amd.CePd_(0.69)Ge_(1.31) is in fact an ordered superstructure of CePd_(0.32)Ge_(1.68) with tripling of the c-lattice.Relative changes in the Pd/Ge ratio also impart substantial variation in their magnetic properties,although Ce is in the trivalent state in both the phases.CePd_(0.21)Ge_(1.79) shows metamagnetic behavior below 10 K whereas CePd_(0.69)Ge_(1.31) showed ferromagnetic behavior in the same temperature range.In addition to the metamagnetic behavior,CePd_(0.21)Ge_(1.79) also shows spin glass behavior at low temperature.DFT calculations were used to obtain ulterior information on the CePd_(0.69)Ge_(1.31) phase.Self-consistent calculations revealed that the ferromagnetic ordering of the ground state arises from the spins at the Ce and Pd sites.The observed sharp rise in the low temperature resistivity of CePd_(0.69)Ge_(1.31) is an indication of a pseudo-gap formation or possible Kondo behavior in the electronic density of states,enhancing the scattering of the charge carriers.Heat capacity measurements on CePd_(0.69)Ge_(1.31) suggest that it falls in the category of medium heavy fermion compounds.
基金The work highlighted in this Account was supported by the Department of Energy,Office of Science,Basic Energy Sciences,under Grant No.SC0012541.L.M.thanks the SUSTech startup grant(Y01216150)P.V.thanks the Science&Engineering Research Board(SERB)of the Govt.of India for the Ramanujan Fellowship(Award No.RJF/2020/000106)the Jawaharlal Nehru Centre for Advanced Scientific Research(JNCASR)Bangalore for the financial support and the research infrastructure.
文摘CONSPECTUS:There is an extensive history of research on both inorganic and hybrid metal halides,with the latter being first reported in the 1960s.Although work on hybrid systems has progressed steadily over the last 60 years,it has enjoyed a major renaissance during the last 5 years.This has arisen as a consequence of the 2009 discovery of the outstanding optoelectronic properties of hybrid lead halides,such as(MA)PbI_(3)(MA=methylammonium),and the recognition that there are many opportunities for equally exciting discoveries with compounds of the transition metals.Some of the early work on hybrid transition-metal halides put more emphasis on crystal structures but less on properties.In the modern era,we aim to grasp both the structure and properties,with a new twist.In this Account,we shall explore the recent developments in hybrid transition-metal halides with a focus on work in four main areas:magnetism,photoluminescence,semiconductivity,and spintronics.Our work on magnetism centers on the Ru-based hybrid halides,where the structural types are diversely composed of vacancy-ordered double perovskite,as well as chain-like one-dimensional structures and layered double perovskite(LDP)when paired with a(1+)metal.We explore their magnetic properties and find that their spin−orbit coupling(SOC)behavior can be tuned through changing the A cation and the halide.In the luminescence section,we focus on our recent works on hybrid tetrahedral Mn(II)bromides and Cu(I)and Ag(I)iodides.We correlated our newly discovered 0D A_(m)MnBr_(4)(A=organic cation,m=1 or 2)compounds with previous reports,and generated a trend where the photoluminescence quantum yield(PLQY)increases with larger Mn−Mn distances.The flexible organic cation becomes the most important tool here to tune the structure−PLQY relations.Cu(I)and Ag(I)iodides coordinated with iodides and organic ligands produce new crystal structures with intense PL.For the semiconducting properties,we explore the Pt-based vacancy-ordered double perovskite and hybrid bismuth and indium-based LDPs to show the structural evolution with different choices for the organic cation,the metal and the halide;these have a strong influence on the optical properties.The LDPs specifically exhibit high structure tunability,with a wide range of(1+)and(3+)metal choices,and are exempt from some of the limitations of 3D double perovskite.In the last section,we introduce the recent progress on hybrid transition-metal-based ferroelectrics and spintronic materials.We successfully demonstrate the utilization of chiral Cu(II)chlorides for circularly polarized light(CPL)detection,showing the high anisotropy of the photoresponsivity.We also highlight the work that the authors have contributed in these areas and suggest several exciting opportunities for future developments.
文摘Sustainable thermoelectric materials open an avenue of emission-free as well as fast-responding recycling of energy in terms of heat to electricity.The efficiency(η)of such conversion is primarily guided by the dimensionless thermoelectric figure of merit(zT),which depends on parameters like Seebeck coefficient(S).
