In this work,Nb^(5+)and Cu^(2+)were selected to partially substitute Zr4+in Gd_(2)Zr_(2)O_(7)for studying the phase structure,microscopic morphology and thermal properties.Gd_(2)(Zr_(1-3 x/2)Nb_(x)CU_(x/2))_(2)O_(7)(x...In this work,Nb^(5+)and Cu^(2+)were selected to partially substitute Zr4+in Gd_(2)Zr_(2)O_(7)for studying the phase structure,microscopic morphology and thermal properties.Gd_(2)(Zr_(1-3 x/2)Nb_(x)CU_(x/2))_(2)O_(7)(x=0,0.05,0.1,0.15,0.2,0.25)ceramic materials were synthesized by high-temperature solid-state reaction method.The results show that the Gd_(2)(Zr_(1-3 x/2)Nb_(x)Cu_(x)/2)_(2)O_(7)ceramics present cubic pyrochlore structure with clear grain boundaries and dense cell structure.And the thermal expansion coefficient of Gd_(2)(Zr_(1-3 x/2)Nb_(x)Cu_(x/2))_(2)O_(7)ceramics gradually decreases because of the incorporation of Nb^(5+)and Cu^(2+)into Zr-site in Gd_(2)Zr_(2)O_(7).Meanwhile,its thermal conductivity decreases firstly and then increases with the doping of Nb^(5+)and Cu^(2+),which reaches the lowest value for the composition of Gd_(2)(Zr_(0.85)Nb_(0.1)Cu_(0.05))_(2)O_(7).展开更多
Ni-rich cathodes exhibit appealing properties,such as high capacity density,low cost,and prominent energy density.However,the inferior ionic conductivity and bulk structural degradation become bottlenecks for Ni-rich ...Ni-rich cathodes exhibit appealing properties,such as high capacity density,low cost,and prominent energy density.However,the inferior ionic conductivity and bulk structural degradation become bottlenecks for Ni-rich cathodes and severely limit their commercial utilization.Traditional coating and doping methods suffer fatal drawbacks in functioning as a unit and cannot radically promote material performance to meet the needs of Li-ion batteries(LIBs).Herein,we successfully devised an ingenious and facile synthetic method to establish Ni-rich oxides with a La_(2)Zr_(2)O_(7) coating and Zr doping.The coating layer improves the ion diffusion kinetics and enhances Li-ion transportation while Zr doping effectively suppresses the phase transition of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) cathode.Owing to the synergetic effect of Zr doping and La_(2)Zr_(2)O_(7) coating,the modified material shows prominent initial discharge capacity of 184.7 m Ah g^(-1) at 5℃ and maintains 177.5 m Ah g^(-1) after 100 cycles at 1℃.Overall,the proposed feasible electrode design method can have a far-reaching impact on further fabrication of advanced cathodes for high-performance LIBs.展开更多
During flight,many silicates(sand,dust,debris,fly ash,etc.)are ingested by an engine.They melt at high operating temperatures on the surface of thermal barrier coatings(TBCs)to form calcium-magnesium-aluminum-silicate...During flight,many silicates(sand,dust,debris,fly ash,etc.)are ingested by an engine.They melt at high operating temperatures on the surface of thermal barrier coatings(TBCs)to form calcium-magnesium-aluminum-silicate(CMAS)amorphous settling.CMAS corrodes TBCs and causes many problems,such as composition segregation,degradation,cracking,and disbanding.As a new generation of TBC candidate materials,rare-earth zirconates(such as Sm_(2)Zr_(2)O_(7))have good CMAS resistance properties.The reaction products of Sm_(2)Zr_(2)O_(7) and CMAS and their subsequent changes were studied by the reaction of Sm_(2)Zr_(2)O_(7) and excess CMAS at 1350℃.After 1 h of reaction,Sm_(2)Zr_(2)O_(7) powders were not completely corroded.The reaction products were Sm-apatite and c-Zr0_(2) solid solution.After 4h of reaction,all Sm_(2)Zr_(2)O_(7) powders were completely corroded.After 24 h of reaction,Sm-apatite disappeared,and the c-Zr02 solid solution remained.展开更多
Environmental sediments mainly consisting of CaO–MgO–Al_(2)O_(3)–SiO_(2)(CMAS)corrosion are a serious threat to thermal barrier coatings(TBCs),in which Fe element is usually ignored.Gd_(2)Zr_(2)O_(7)TBCs are famous...Environmental sediments mainly consisting of CaO–MgO–Al_(2)O_(3)–SiO_(2)(CMAS)corrosion are a serious threat to thermal barrier coatings(TBCs),in which Fe element is usually ignored.Gd_(2)Zr_(2)O_(7)TBCs are famous for their excellent CMAS resistance.In this study,the characteristics of Fe-containing environmental sediments(CMAS-Fe)and their corrosiveness to Gd_(2)Zr_(2)O_(7)coatings were investigated.Four types of CMAS-Fe glass with different Fe contents were fabricated.Their melting points were measured to be 1322–1344℃,and the high-temperature viscosity showed a decreasing trend with increasing Fe contents.The corrosion behavior of four types of CMAS-Fe to Gd_(2)Zr_(2)O_(7)coatings at 1350℃was investigated.At the initial corrosion stage(0.1 h),anorthite was precipitated in CMAS-Fe with a high Ca:Si ratio,while Fe-garnet was formed in the melt with the highest Fe content.Prolonging the corrosion time resulted in the formation of a reaction layer,which exhibited an interpenetrating network composed of Gd-oxyapatite,ZrO_(2),and residual CMAS-Fe.Some spinel was precipitated within the reaction layer.After 1 h or even longer time,the reaction layers tended to be stable and compact,which had comparable hardness and fracture toughness to those of Gd_(2)Zr_(2)O_(7)coatings.Under the cyclic CMAS-Fe attack,the residual CMAS-Fe in the interpenetrating network provided a pathway for the redeposited CMAS-Fe infiltration,resulting in the continuous growth of the reaction layer.As a result,the Gd_(2)Zr_(2)O_(7)coatings had a large consumption in the thickness,degrading the coating performance.Therefore,the Gd_(2)Zr_(2)O_(7)coatings exhibit unsatisfactory corrosion resistance to CMAS-Fe attack.展开更多
First-principles calculations based on density functional theory were perfo rmed to investigate the cohesive energies,elastic modulus,Debye temperatures,thermal conductivities and density of states of La_(2-x)Yb_(x)Zr...First-principles calculations based on density functional theory were perfo rmed to investigate the cohesive energies,elastic modulus,Debye temperatures,thermal conductivities and density of states of La_(2-x)Yb_(x)Zr_(2)O_(7),La_(2)Zr_(2-x)Ce_(x)O_(7)and La_(2-x)Yb_(x)Zr_(2-x)Ce_(x)O_(7)(x=0.00,0.25,0.50,0.75,1.00)ceramics.The results show that doping Yb~(3+)or Ce~(4+)into La_(2)Zr_(2)O_(7)reduces its elastic modulus,thermal conductivity and Debye temperature.Compared with La_(2-x)Yb_(x)Zr_(2)O_(7)(x≠0.00),La_(2)Zr_(2-x)Ce_(x)O_(7)compounds have better ductility and lower Debye te mperature.The Debye temperature values of La_(2)Zr_(2-x)Ce_(x)O_(7)(x≠0.00)co mpounds are in the range of 485.0-511.5 K.Among all components,the fluorite-type La_(2-x)Yb_(x)Zr_(2-x)Ce_(x)O_(7)(x=0.75,1.00)compounds exhibit better mechanical and thermophysical properties,and their thermal conductivity values are only 1.213-1.246 W/(m·K)(1073 K),which are 14.5%-16.7%lower than that of the pure La_(2)Zr_(2)O_(7).Thus,our findings open an entirely new avenue for TBCs.展开更多
Although rare earth zirconates(RE_(2)Zr_(2)O_(7))have garnered attention as viable candidates for thermal barrier coatings(TBCs),they suffer from low fracture toughness and accelerated calcium–magnesium–alumina–sil...Although rare earth zirconates(RE_(2)Zr_(2)O_(7))have garnered attention as viable candidates for thermal barrier coatings(TBCs),they suffer from low fracture toughness and accelerated calcium–magnesium–alumina–silicate(CMAS)melt corrosion at high service temperatures,which impedes their practical application.In this work,we developed a series of REAlO_(3)/RE_(2)Zr_(2)O_(7)(RE=La,Nd,Sm,Eu,Gd,and Dy)composites with a eutectic composition that not only significantly enhanced the fracture toughness by more than 40%relative to that of RE_(2)Zr_(2)O_(7)but also exhibited improved resistance to CMAS corrosion.The increase in toughness arises from multiple mechanisms,such as ferroelastic toughening,fine-grain strengthening,and residual stress toughening,all of which trigger more crack defects and energy consumption.Additionally,the CMAS penetration depth of the REAlO_(3)/RE_(2)Zr_(2)O_(7)composites is approximately 36%lower than that of RE_(2)Zr_(2)O_(7).Al–O constituents in composites can capture CaO,SiO_(2),and MgO in CMAS melts and increase their viscosity,resulting in enhanced CMAS corrosion resistance.The thermophysical properties of the REAlO_(3)/RE_(2)Zr_(2)O_(7)composites were also investigated,and their coefficient of thermal expansion and thermal conductivity are comparable to those of 7–8 wt%Y_(2)O_(3)partially stabilized ZrO2(YSZ),indicating their potential as TBC materials.展开更多
Based on material design idea,we employ a co-precipitation strategy to obtain sinterable Ho_(2)Zr_(2)O_(7) flu-orite particles,successfully leading to novel transparent Ho_(2)Zr_(2)O_(7) ceramics with good optical/mag...Based on material design idea,we employ a co-precipitation strategy to obtain sinterable Ho_(2)Zr_(2)O_(7) flu-orite particles,successfully leading to novel transparent Ho_(2)Zr_(2)O_(7) ceramics with good optical/magneto-optical properties.The resulting precipitation precursor is identified to be hydrated basic carbonate upon calcination at the optimum temperature of 1250℃into near-spherical Ho_(2)Zr_(2)O_(7) nanopowder with an average size of~64 nm and unimodal narrow size distribution.The crystal intrinsic oxygen defect in fluorite ceramic generally exists in the form of F+center.The best bulk specimen achieved in this work exhibits a high refractive index of~2.1 and a high transparency of~74.4%at 1000 nm comparable with the corresponding defect-free single crystal(~76.4%in theory).In the Ho_(2)Zr_(2)O_(7) structure system,the elec-tronic polarizability of O_(2)-anion generally remains constant around 2.2?3 in the visible region and the corresponding optical basicity is approximately 0.9.The developed magneto-optical transparent Ho_(2)Zr_(2)O_(7) ceramic has Verdet constants of-180±3,-157±5,-87±2,-54±2,and-43±2 rad T^(-1) m^(-1) at 515,635,780,980,and 1064 nm,respectively,which are roughly 1.2-fold higher than the commercial TGG crystal.展开更多
Developing new high-entropy rare-earth zirconate(HE-RE_(2)Zr_(2)O_(7))ceramics with low thermal conductivity is essential for thermal barrier coating materials.In this work,the average atomic spacings,interatomic forc...Developing new high-entropy rare-earth zirconate(HE-RE_(2)Zr_(2)O_(7))ceramics with low thermal conductivity is essential for thermal barrier coating materials.In this work,the average atomic spacings,interatomic forces,and average atomic masses of 16 rare-earth elements occupying the A site of the cubic A_(2)B_(2)O_(7) crystal structure were calculated by density functional theory.These three physical qualities,as vectors,characterize the corresponding rare-earth elements.The distance between two vectors quantitatively describes the difference between two rare-earth elements.For greater differences between two rare-earth elements,the disorder degree of HE-RE_(2)Zr_(2)O_(7)is greater,and therefore,the thermal conductivity is lower.According to the theoretical calculations,the thermal conductivity of the ceramics gradually increases in the order of(SC_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Ce_(0.2)Nd_(0.2)Eu_(0.2)Gd_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Y_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)0_(7),and(Sc_(0.2)Er_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)O_(7).Using the solution precursor plasma spray method and pressureless sintering method,four types of HE-RE2Zr2Oz powder and bulk samples were prepared.The samples all showed a single defective fluorite structure with a uniform distribution of the elements and a stable phase structure.The thermal conductivities of the sintered HE-RE_(2)Zr_(2)0_(7) bulk samples ranged from 1.30 to 1.45 Wm^(-1).K^(-1) at 1400℃,and their differences were consistent with the theoretical calculation results.Among the ceramics,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7) had the lowest thermal conductivity(1.30 W·m^(-1)·K^(-1),1400℃),highest thermal expansion coefficient(10.19×10^(-6) K^(-1),200-1400℃),highest fracture toughness(1.69±0.28 MPa·m^(1/2)),and smallest brttleness index(3.03μm^(1/2)).Therefore,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7)is considered to be an ideal candidate material for next-generation thermal barrier coat展开更多
At present,the high re-combination rate of photogenerated carriers and the low redox capability of the photocatalyst are two factors that severely limit the improvement of photocatalytic performance.Herein,a dual Z-sc...At present,the high re-combination rate of photogenerated carriers and the low redox capability of the photocatalyst are two factors that severely limit the improvement of photocatalytic performance.Herein,a dual Z-scheme photocatalyst bismuthzirconate/graphitic carbon nitride/silver phosphate (Bi_(2)Zr_(2)O_(7)/g-C_(3)N4/Ag_(3)PO_(4)(BCA)) was synthesized using a co-precipitation method,and a dual Z-scheme heterojunction photocatalytic system was established to decrease the high re-combination rate of photogenerated carriers and consequently improve the photocatalytic performance.The re-combination of electron-hole pairs(e-and h+) in the valence band (VB) of g-C_(3)N4increases the redox potential of e-and h+,leading to significant improvements in the redox capability of the photocatalyst and the efficiency of e--h+separation.As a photosensitizer,Ag_(3)PO_(4)can enhance the visible light absorption capacity of the photocatalyst.The prepared photocatalyst showed strong stability,which was attributed to the efficient suppression of photo-corrosion of Ag_(3)PO_(4)by transferring the e-to the VB of g-C_(3)N4.Tetracycline was degraded efficiently by BCA-10%(the BCA with 10 wt.%of AgPO_(4)) under visible light,and the degradation efficiency was up to 86.2%.This study experimentally suggested that the BCA photocatalyst has broad application prospects in removing antibiotic pollution.展开更多
基金the National Natural Science Foundation of China(51762036)。
文摘In this work,Nb^(5+)and Cu^(2+)were selected to partially substitute Zr4+in Gd_(2)Zr_(2)O_(7)for studying the phase structure,microscopic morphology and thermal properties.Gd_(2)(Zr_(1-3 x/2)Nb_(x)CU_(x/2))_(2)O_(7)(x=0,0.05,0.1,0.15,0.2,0.25)ceramic materials were synthesized by high-temperature solid-state reaction method.The results show that the Gd_(2)(Zr_(1-3 x/2)Nb_(x)Cu_(x)/2)_(2)O_(7)ceramics present cubic pyrochlore structure with clear grain boundaries and dense cell structure.And the thermal expansion coefficient of Gd_(2)(Zr_(1-3 x/2)Nb_(x)Cu_(x/2))_(2)O_(7)ceramics gradually decreases because of the incorporation of Nb^(5+)and Cu^(2+)into Zr-site in Gd_(2)Zr_(2)O_(7).Meanwhile,its thermal conductivity decreases firstly and then increases with the doping of Nb^(5+)and Cu^(2+),which reaches the lowest value for the composition of Gd_(2)(Zr_(0.85)Nb_(0.1)Cu_(0.05))_(2)O_(7).
基金supported by the National Natural Science Foundation of China(Grant No.51974368)the Fundamental Research Funds for the Central Universities of Central South University(2019zzts251)。
文摘Ni-rich cathodes exhibit appealing properties,such as high capacity density,low cost,and prominent energy density.However,the inferior ionic conductivity and bulk structural degradation become bottlenecks for Ni-rich cathodes and severely limit their commercial utilization.Traditional coating and doping methods suffer fatal drawbacks in functioning as a unit and cannot radically promote material performance to meet the needs of Li-ion batteries(LIBs).Herein,we successfully devised an ingenious and facile synthetic method to establish Ni-rich oxides with a La_(2)Zr_(2)O_(7) coating and Zr doping.The coating layer improves the ion diffusion kinetics and enhances Li-ion transportation while Zr doping effectively suppresses the phase transition of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) cathode.Owing to the synergetic effect of Zr doping and La_(2)Zr_(2)O_(7) coating,the modified material shows prominent initial discharge capacity of 184.7 m Ah g^(-1) at 5℃ and maintains 177.5 m Ah g^(-1) after 100 cycles at 1℃.Overall,the proposed feasible electrode design method can have a far-reaching impact on further fabrication of advanced cathodes for high-performance LIBs.
基金supported by the National Natural Science Foundation of China(No.5177020526).
文摘During flight,many silicates(sand,dust,debris,fly ash,etc.)are ingested by an engine.They melt at high operating temperatures on the surface of thermal barrier coatings(TBCs)to form calcium-magnesium-aluminum-silicate(CMAS)amorphous settling.CMAS corrodes TBCs and causes many problems,such as composition segregation,degradation,cracking,and disbanding.As a new generation of TBC candidate materials,rare-earth zirconates(such as Sm_(2)Zr_(2)O_(7))have good CMAS resistance properties.The reaction products of Sm_(2)Zr_(2)O_(7) and CMAS and their subsequent changes were studied by the reaction of Sm_(2)Zr_(2)O_(7) and excess CMAS at 1350℃.After 1 h of reaction,Sm_(2)Zr_(2)O_(7) powders were not completely corroded.The reaction products were Sm-apatite and c-Zr0_(2) solid solution.After 4h of reaction,all Sm_(2)Zr_(2)O_(7) powders were completely corroded.After 24 h of reaction,Sm-apatite disappeared,and the c-Zr02 solid solution remained.
基金the National Natural Science Foundation of China(Grant No.52272070)National Science and Technology Major Project(Grant No.J2022-VI-0009-0040).
文摘Environmental sediments mainly consisting of CaO–MgO–Al_(2)O_(3)–SiO_(2)(CMAS)corrosion are a serious threat to thermal barrier coatings(TBCs),in which Fe element is usually ignored.Gd_(2)Zr_(2)O_(7)TBCs are famous for their excellent CMAS resistance.In this study,the characteristics of Fe-containing environmental sediments(CMAS-Fe)and their corrosiveness to Gd_(2)Zr_(2)O_(7)coatings were investigated.Four types of CMAS-Fe glass with different Fe contents were fabricated.Their melting points were measured to be 1322–1344℃,and the high-temperature viscosity showed a decreasing trend with increasing Fe contents.The corrosion behavior of four types of CMAS-Fe to Gd_(2)Zr_(2)O_(7)coatings at 1350℃was investigated.At the initial corrosion stage(0.1 h),anorthite was precipitated in CMAS-Fe with a high Ca:Si ratio,while Fe-garnet was formed in the melt with the highest Fe content.Prolonging the corrosion time resulted in the formation of a reaction layer,which exhibited an interpenetrating network composed of Gd-oxyapatite,ZrO_(2),and residual CMAS-Fe.Some spinel was precipitated within the reaction layer.After 1 h or even longer time,the reaction layers tended to be stable and compact,which had comparable hardness and fracture toughness to those of Gd_(2)Zr_(2)O_(7)coatings.Under the cyclic CMAS-Fe attack,the residual CMAS-Fe in the interpenetrating network provided a pathway for the redeposited CMAS-Fe infiltration,resulting in the continuous growth of the reaction layer.As a result,the Gd_(2)Zr_(2)O_(7)coatings had a large consumption in the thickness,degrading the coating performance.Therefore,the Gd_(2)Zr_(2)O_(7)coatings exhibit unsatisfactory corrosion resistance to CMAS-Fe attack.
基金Project supported by the National Natural Science Foundation of China(52071172,51361026)the Key Research&Developement Plan of Jiangxi Province(20203BBE53046,20181ACH80009)+1 种基金the China Postdoctoral Science Foundation(2017M620576)the Aeronautical Science Foundation of China(2017ZE56015)。
文摘First-principles calculations based on density functional theory were perfo rmed to investigate the cohesive energies,elastic modulus,Debye temperatures,thermal conductivities and density of states of La_(2-x)Yb_(x)Zr_(2)O_(7),La_(2)Zr_(2-x)Ce_(x)O_(7)and La_(2-x)Yb_(x)Zr_(2-x)Ce_(x)O_(7)(x=0.00,0.25,0.50,0.75,1.00)ceramics.The results show that doping Yb~(3+)or Ce~(4+)into La_(2)Zr_(2)O_(7)reduces its elastic modulus,thermal conductivity and Debye temperature.Compared with La_(2-x)Yb_(x)Zr_(2)O_(7)(x≠0.00),La_(2)Zr_(2-x)Ce_(x)O_(7)compounds have better ductility and lower Debye te mperature.The Debye temperature values of La_(2)Zr_(2-x)Ce_(x)O_(7)(x≠0.00)co mpounds are in the range of 485.0-511.5 K.Among all components,the fluorite-type La_(2-x)Yb_(x)Zr_(2-x)Ce_(x)O_(7)(x=0.75,1.00)compounds exhibit better mechanical and thermophysical properties,and their thermal conductivity values are only 1.213-1.246 W/(m·K)(1073 K),which are 14.5%-16.7%lower than that of the pure La_(2)Zr_(2)O_(7).Thus,our findings open an entirely new avenue for TBCs.
基金supported by the National Key R&D Program of China(No.2021YFB3702300)the National Natural Science Foundation of China(No.52022042)+2 种基金the Project of the Science Center for Gas Turbine(No.HT-P2022-DB-Ⅳ-002-001)the National Science and Technology Major Project(No.J2019-Ⅶ−0008-0148)the Research on the Development and Preparation of Thermal Barrier Coating Materials on New Generation of Heavy-duty Gas Turbines(No.UGTC-HT-WXKT-2022-032).
文摘Although rare earth zirconates(RE_(2)Zr_(2)O_(7))have garnered attention as viable candidates for thermal barrier coatings(TBCs),they suffer from low fracture toughness and accelerated calcium–magnesium–alumina–silicate(CMAS)melt corrosion at high service temperatures,which impedes their practical application.In this work,we developed a series of REAlO_(3)/RE_(2)Zr_(2)O_(7)(RE=La,Nd,Sm,Eu,Gd,and Dy)composites with a eutectic composition that not only significantly enhanced the fracture toughness by more than 40%relative to that of RE_(2)Zr_(2)O_(7)but also exhibited improved resistance to CMAS corrosion.The increase in toughness arises from multiple mechanisms,such as ferroelastic toughening,fine-grain strengthening,and residual stress toughening,all of which trigger more crack defects and energy consumption.Additionally,the CMAS penetration depth of the REAlO_(3)/RE_(2)Zr_(2)O_(7)composites is approximately 36%lower than that of RE_(2)Zr_(2)O_(7).Al–O constituents in composites can capture CaO,SiO_(2),and MgO in CMAS melts and increase their viscosity,resulting in enhanced CMAS corrosion resistance.The thermophysical properties of the REAlO_(3)/RE_(2)Zr_(2)O_(7)composites were also investigated,and their coefficient of thermal expansion and thermal conductivity are comparable to those of 7–8 wt%Y_(2)O_(3)partially stabilized ZrO2(YSZ),indicating their potential as TBC materials.
基金supported by the Zhejiang Provincial Natural Science Foundation of China (Grant No.LY23F050007)the Department of Education of Zhejiang Province (No.Y202146207).
文摘Based on material design idea,we employ a co-precipitation strategy to obtain sinterable Ho_(2)Zr_(2)O_(7) flu-orite particles,successfully leading to novel transparent Ho_(2)Zr_(2)O_(7) ceramics with good optical/magneto-optical properties.The resulting precipitation precursor is identified to be hydrated basic carbonate upon calcination at the optimum temperature of 1250℃into near-spherical Ho_(2)Zr_(2)O_(7) nanopowder with an average size of~64 nm and unimodal narrow size distribution.The crystal intrinsic oxygen defect in fluorite ceramic generally exists in the form of F+center.The best bulk specimen achieved in this work exhibits a high refractive index of~2.1 and a high transparency of~74.4%at 1000 nm comparable with the corresponding defect-free single crystal(~76.4%in theory).In the Ho_(2)Zr_(2)O_(7) structure system,the elec-tronic polarizability of O_(2)-anion generally remains constant around 2.2?3 in the visible region and the corresponding optical basicity is approximately 0.9.The developed magneto-optical transparent Ho_(2)Zr_(2)O_(7) ceramic has Verdet constants of-180±3,-157±5,-87±2,-54±2,and-43±2 rad T^(-1) m^(-1) at 515,635,780,980,and 1064 nm,respectively,which are roughly 1.2-fold higher than the commercial TGG crystal.
基金This work is supported by the National Natural Science Foundation of China(Nos.51865044,52062040)Science and Technology Projects of Inner Mongolia Autonomous Region(Nos.2021PT0008,2022ZD02,2022MS05003)Basic Scientific Research Expenses Program of Universities Directly under Inner Mongolia Autonomous Region(Nos.JY20220041,JY20220062).
文摘Developing new high-entropy rare-earth zirconate(HE-RE_(2)Zr_(2)O_(7))ceramics with low thermal conductivity is essential for thermal barrier coating materials.In this work,the average atomic spacings,interatomic forces,and average atomic masses of 16 rare-earth elements occupying the A site of the cubic A_(2)B_(2)O_(7) crystal structure were calculated by density functional theory.These three physical qualities,as vectors,characterize the corresponding rare-earth elements.The distance between two vectors quantitatively describes the difference between two rare-earth elements.For greater differences between two rare-earth elements,the disorder degree of HE-RE_(2)Zr_(2)O_(7)is greater,and therefore,the thermal conductivity is lower.According to the theoretical calculations,the thermal conductivity of the ceramics gradually increases in the order of(SC_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Ce_(0.2)Nd_(0.2)Eu_(0.2)Gd_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Y_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)0_(7),and(Sc_(0.2)Er_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)O_(7).Using the solution precursor plasma spray method and pressureless sintering method,four types of HE-RE2Zr2Oz powder and bulk samples were prepared.The samples all showed a single defective fluorite structure with a uniform distribution of the elements and a stable phase structure.The thermal conductivities of the sintered HE-RE_(2)Zr_(2)0_(7) bulk samples ranged from 1.30 to 1.45 Wm^(-1).K^(-1) at 1400℃,and their differences were consistent with the theoretical calculation results.Among the ceramics,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7) had the lowest thermal conductivity(1.30 W·m^(-1)·K^(-1),1400℃),highest thermal expansion coefficient(10.19×10^(-6) K^(-1),200-1400℃),highest fracture toughness(1.69±0.28 MPa·m^(1/2)),and smallest brttleness index(3.03μm^(1/2)).Therefore,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7)is considered to be an ideal candidate material for next-generation thermal barrier coat
基金the financial support provided by the Shandong University Cross Project fund (No.2016JC003)。
文摘At present,the high re-combination rate of photogenerated carriers and the low redox capability of the photocatalyst are two factors that severely limit the improvement of photocatalytic performance.Herein,a dual Z-scheme photocatalyst bismuthzirconate/graphitic carbon nitride/silver phosphate (Bi_(2)Zr_(2)O_(7)/g-C_(3)N4/Ag_(3)PO_(4)(BCA)) was synthesized using a co-precipitation method,and a dual Z-scheme heterojunction photocatalytic system was established to decrease the high re-combination rate of photogenerated carriers and consequently improve the photocatalytic performance.The re-combination of electron-hole pairs(e-and h+) in the valence band (VB) of g-C_(3)N4increases the redox potential of e-and h+,leading to significant improvements in the redox capability of the photocatalyst and the efficiency of e--h+separation.As a photosensitizer,Ag_(3)PO_(4)can enhance the visible light absorption capacity of the photocatalyst.The prepared photocatalyst showed strong stability,which was attributed to the efficient suppression of photo-corrosion of Ag_(3)PO_(4)by transferring the e-to the VB of g-C_(3)N4.Tetracycline was degraded efficiently by BCA-10%(the BCA with 10 wt.%of AgPO_(4)) under visible light,and the degradation efficiency was up to 86.2%.This study experimentally suggested that the BCA photocatalyst has broad application prospects in removing antibiotic pollution.
