反钙钛矿结构Mn_3Ga_(0.503)Ge_(0.497)N金属化合物的性能

采用氮气保护气氛下固相烧结法制备出Mn_3Ga_(0.503)Ge_(0.497)N化合物,并对其性能进行了测试。通过多晶粉末X射线衍射进行了结构表征和热膨胀性能测试,结果表明:具有立方反钙钛矿结构的Mn_3Ga_(0.503)Ge_(0.497)N化合物在420~470 K温度范围内表现出负热膨胀性能,其平均热膨胀系数为-13.3×10~(-6)K~(-1)。磁性测试结果表明:Mn_3Ga_(0.503)Ge_(0.497)N化合物在457 K左右发生了顺磁-铁磁的磁性转变。力学性能测试结果表明:其维氏硬度范围为450~480 HV,抗压强度和压缩弹性模量分别为350 MPa和2.48 GPa,是一种高硬度脆性陶瓷材料,可以用来制造具有轻质、刚性、低膨胀和高加工性的器件。     

一步法合成La_(0.4)Sr_(0.6)Co_(0.2)Fe_(0.7)Nb_(0.1)O_(3-δ)-Ce_(0.8)Gd_(0.2)O_(2-δ)对称电极应用于SOFC性能研究

一步法合成La_(0.4)Sr_(0.6)Co_(0.2)Fe_(0.7)Nb_(0.1)O_(3-δ)-Ce_(0.8)Gd_(0.2)O_(2-δ)(LSCFN-CGO)混合电导对称电极,并采用La_(0.8)Sr_(0.2)Ga_(0.83)Mg_(0.17)O_(3-δ)(LSGM)作为电解质制备了结构为LSCFN-CGO‖_(LSGM)‖LSCFN-CGO的对称电池。分别使用X射线衍射(XRD)仪和扫描电子显微镜(SEM)对LSCFN-CGO粉体物相及电极微观结构进行分析。一步法制得的LSCFN-CGO电极粉体为纯相,LSCFN钙钛矿相与CGO萤石相具备极好的化学相容性,且烧结得到了良好微观结构的对称电极。采用H_2 (3%H_2O)、C_3H_8 (3%H_2O)为燃料气测试电池性能,850℃电池最大功率密度可分别达980和869mW/cm~2。稳定性测试在C_3H_8 (3%H_2O)气氛中0.3 A/cm~2的恒流放电条件下进行,全程共420 h,衰减较小,期间进行8次电极氧化还原循环,对称电极具有理想的碳基燃料下氧化还原再生能力。结果表明,采用一步法合成混合电导电极是一种简便、优化的电极制备方法,具有广阔的应用前景。     

MnFeP_(0.63)Ge(0.12)Si_(0.25)B_x(x=0,0.01,0.02,0.03)化合物的磁热效应

对MnFeP_(0.63)Ge_(0.12)Si_(0.25)B_x(x=0,0.01,0.02,0.03,原子分数)化合物的结构和磁热效应(MCE)进行了研究.XRD分析结果表明:MnFeP_(0.63)Ge_(0.12)Si_(0.25)B_x(x=0,0.01,0.02,0.03)的主相均为Fe_2P型六角结构,空间群为P62m.随着B含量的增加晶格常数a增大c减小,晶胞体积基本保持不变.磁性测量表明:随着B含量由0增加到0.03时,Curie温度(T_C)从300 K升到347 K,热滞分别为20,17,11和6 K.0-1.5 T外磁场下最大磁熵变△S_M分别为14.83,11.41,11.26和11.8 J/(kg·K).     

Mn含量对Mn_(2-x)Sn_(0.5)Ga_(0.5) Heusler合金磁及磁热性能的影响

选用Mn基Heusler合金为研究对象,通过电弧熔炼和热处理制备样品,并用甩带法制成薄带形状。采用X射线衍射仪和振动样品磁强计等分析仪器测试样品的晶体结构、磁及磁热性能,分析Mn含量对材料晶体结构、磁和磁热性能的影响。结果表明,Mn_(2-x)Sn_(0.5)Ga_(0.5)合金在室温下为六方结构,在室温附近仅发生一次二阶磁性转变,无明显磁滞和热滞。居里温度和饱和磁化强度对Mn含量非常敏感,随着Mn含量升高,居里温度和饱和磁化强度均出现下降,由Mn~(1.2)Sn_(0.5)Ga_(0.5)的304 K和64.1 A·m~2·kg~(-1)分别降至Mn_2Sn_(0.5)Ga_(0.5)的262 K和46.7 A·m2·kg~(-1),这表明合金中的磁矩呈亚铁磁形态分布。由于没有磁滞和热滞,室温附近具有较大的工作温度区间,所以该材料在磁制冷领域具有很好的应用前景。     

Fe_(83)Ga_(17)R_(0.6)(R=Ce,Tb,Dy)合金的微结构与磁致伸缩性能

为改善多晶Fe-Ga合金的磁致伸缩性能,在Fe-Ga合金中掺杂稀土Ce、Tb和Dy元素。研究了Fe_(83)Ga_(17)和Fe_(83)Ga_(17)R_(0.6)(R=Ce,Tb,Dy)合金的相结构和磁致伸缩性能。结果表明,Fe_(83)Ga_(17)合金由单一bcc结构Fe(Ga)固溶体相组成,而掺杂稀土后的Fe_(83)Ga_(17)R_(0.6)合金中除保持bcc结构的Fe(Ga)固溶体相外,还出现了R_2Fe_(17)第二相。掺杂稀土后的Fe_(83)Ga_(17)R_(0.6)合金磁致伸缩系数明显大于Fe_(83)Ga_(17)合金。掺杂不同种类的稀土元素对Fe-Ga合金磁致伸缩性能改善的程度不同。在外磁场为557 k A/m时,Fe_(83)Ga_(17)R_(0.6)合金的磁致伸缩系数(206×10~(-6))明显大于Fe_(83)Ga_(17)Tb_(0.6)(165×10~(-6))和FFe_(83)Ga_(17)Dy_(0.6)(161×10~(-6))合金的磁致伸缩系数。     

粉煤灰中锗的高温火法二次富集工艺

采用高温火法二次富集工艺对含锗粉煤灰中的锗进行富集,以锗含量为0.35%(质量分数)的粉煤灰为原料,研究温度、C含量、碱度、保温时间等工艺参数,对高温火法二次富集工艺锗的富集的影响。结果表明:当粉煤灰中碳含量为3%,碱度为1.0,在1600℃下保温1 h可以取得较好的锗富集效果。富集物中锗含量可达到16.65%,富集物中锗的收得率达到89.55%。对富集后的富集物和渣进行XRD物相分析,富集后锗以锗酸盐(Ca_2Ge O_4和Ca_2Ge_7O_(16))和FeGe形式在富集物中存在,渣呈玻璃相,有利于锗的提取。     

孔隙率对SFN-LSGM作为SOEC阴极的性能影响

选择具有双钙钛矿结构的Sr_2Fe Nb O_6(SFN)及La_(0.9)Sr_(0.1)Ga_(0.8)Mg_(0.2)O_(3-δ)(LSGM)材料混合作为固体氧化物电解池(SOEC)的阴极,在SFN-LSGM中掺杂不同比例的淀粉,经过干压成型并在1400℃下烧结后得到测试样。利用真实密度仪及阿基米德法测定了样品的孔隙率;利用热分析仪测定了不同孔隙率的样品在35~1400℃条件下的热膨胀系数,研究该材料与常用SOEC电解质材料La0.9Sr0.1Ga0.8Mg0.2O3-δ(LSGM)的热匹配性能;之后利用电化学工作站测试了该材料在纯氢气气氛下电导率与孔隙率的关系。结果表明,样品孔隙率与淀粉掺杂量成正比,孔隙率对该材料热膨胀系数影响不大,且该材料与LSGM电解池热匹配性能良好。另外,当样品孔隙率增加时,该材料在850℃纯氢气气氛下的电导率在18%孔隙率时达到最大值。     

微波快速合成-烧结制备ZrNiSn半赫斯勒热电合金

开展了ZrNiSn热电块体材料的微波快速合成-烧结研究,并对样品的物相组成、电性能、热性能、微观结构和综合热电性能进行了测试和表征分析。相组成分析表明,采用微波固相合成在4~5 min内即获得了单一相纯度很高的ZrNiSn合金,但存在少量杂质Sn;合成样品经30 min微波烧结后,部分Sn因二次反应而消除。电性能分析表明,电阻率较高为13.7~16.9μ?·m,从而对功率因子产生较大影响,功率因子最高为1683μW·m~(-1)·K~(-2)。热性能分析表明,ZrNiSn样品的热导率随着温度升高而降低,热导率最大为4.288 W·m~(-1)·K~(-1),晶格热导率仅为2.86~3.96 W·m~(-1)·K~(-1),热性能良好。微观结构分析表明,微波烧结抑制了ZrNiSn晶粒长大,ZrNiSn基体晶内和晶界分布有大量纳米晶粒,绝大部分属于晶内析出,且分布较均匀,少部分分布在晶界。综合热电性能ZT值随测试温度的增加显著上升,在573~673 K获得最大值0.25。     

铝酸镧掺杂对Ba_(0.6)Sr_(0.4)TiO_3介电性能的影响

在外加直流偏置电场作用下,钛酸锶钡(BST)固溶体铁电材料具有随着电场强度增加而介电常数降低的非线性特征,是相控阵天线移相器材料的研究热点.而铝酸镧陶瓷介电常数温度系数可达接近零,介电损耗正切值低,可小于1×10~(-4).为降低BST材料的介电损耗和介电常数,以铝酸镧为改性剂对Ba_0.6Sr_0.4TiO_3材料进行了掺杂.当铝酸镧的含量为4%时,Ba_0.6Sr_0.4TiO_3材料的介电常数降低到85(100 kHz),介电损耗降低到0.00041(100 kHz),而Ba_0.6Sr_0.4TiO_3材料的介电可调性保持在20%左右.X射线衍射图谱表明烧结后得到的BST材料具有典型的钙钛矿结构. SEM图像观察发现,4%比例的掺杂量使得陶瓷致密度较高,晶粒均匀.     

Bi掺杂Ba_(0.6)Sr_(0.4)CeO_3电解质材料的导电性研究

Ba_(0.6)Sr_(0.4)CeO_3具有特殊的质子传导特征,可作为新型电解质材料应用于中低温燃料电池。主要研究了Bi掺杂对Ba_(0.6)Sr_(0.4)CeO_3材料电导率的影响及其相关机理。采用高温固相法合成了不同Bi掺杂量的Ba0.6Sr0.4Ce1-xBixO3(x=0,0.05,0.1,0.2)粉体。利用XRD及SEM分析了Bi掺杂量对材料物相组成和断口形貌的影响。通过电化学工作站分别测试了Ba0.6Sr0.4Ce1-xBixO3在空气和氢气气氛下的电导率,并分析了材料在不同气氛下的导电机制。结果表明:不同掺杂量的Ba0.6Sr0.4Ce1-xBixO3在空气中1300℃下保温10 h均可形成结构单一且气密性较高的电解质。掺杂Bi可有效提高Ba_(0.6)Sr_(0.4)CeO_3体系的电导率,当Bi掺杂量x为0.2时,Ba0.6Sr0.4Ce0.8Bi0.2O3电导率最高。在氢气气氛下,700℃时,Ba0.6Sr0.4Ce0.8Bi0.2O3的电导率达到了9.1×10-3 S·cm-1。     

Structural disorder and thermal conductivity of the semiconducting clathrate Sr8Ga16Ge30

The temperature dependence of the atomic displacement parameters for Sr₈Ga₁₆Ge₃₀ determined from refinements of neutron powder and single-crystal diffraction data shows that the anomalously large values for one of the two unique Sr atoms persist from 295 to 11 K. Its position is better described by a fractionally occupied four-fold split site, but the rms displacement remains the largest of all of the atoms in the structure. Difference Fourier maps of this Sr site show a residual nuclear density with lobes in the directions of the split-atom positions. The Ga and Ge atoms appear to be fully disordered on the three distinct framework sites. The measured atomic displacement parameters are used to derive estimates of the following thermodynamic related quantities: Debye temperature, 271 K; mean velocity of sound, 2600 m/s; temperature of the Einstein “rattler”, 85 K; mean free path of heat-carrying phonons, 5.36 Å; and lattice thermal conductivity, 0.008 W/cm-K.     

Mechanisms of linear anelasticity in Fe-M and Fe-Al-M (M = Ga, Ge) alloys

Linear anelastic effects in binary and ternary alloys of iron with 13 and 17 at % Ga, 12 at % Ge, and 4–8 at % Al (Fe-13Ga, Fe-17Ga, Fe-12Ge, Fe-8Al-3Ga, Fe-8Al-4Ge, and Fe-4Al-8Ge) have been investigated. In all of these alloys, thermally activated effects of linear anelasticity have been found and identified that are caused by point defects in interstitial (Snoek-type relaxation) and substitutional (Zener relaxation) solid solutions, as well as by dislocations (Hasiguti effect), and by grain boundaries. The effects of the alloy composition on the activation parameters of the above-mentioned relaxation mechanisms have been determined. In addition, frequency-independent effects related to processes of structural rearrangement, such as ordering and disordering of the alloys have been revealed due to the specific features in the curves of the temperature dependences of internal friction for almost all compositions.     

Splitting of guest atom sites and lattice thermal conductivity of type-I and type-III clathrate compounds in the Ba–Ga–Ge system

The crystal structures of type-I and type-III clathrate compounds in the Ba–Ga–Ge system have been investigated by synchrotron X-ray powder diffraction at room temperature with single- and split-site models to describe thermal vibration of the Ba atoms that are believed to ‘rattle’ in the encapsulating cages. The split-site model is verified to be more plausible when judged from the changes of the extent of thermal vibration of the Ba atoms and the shape changes of the encapsulating cages with the Ga content for both types of compound. When described with the split-site model, the value of lattice thermal conductivity at room temperature decreases with increasing split distance of the Ba atom site for both types of compound, indicating that the split distance can be used as a parameter to describe the extent of thermal vibration (rattling motion) of the Ba guest atoms in the encapsulating cages.     

Effects of Solute Atoms on 9R Phase Stabilization in High-Performance Al Alloys: A First-Principles Study

Recent experiments have proven that the 9R phase can dramatically improve the mechanical properties of Al alloys. This work aims to investigate the effects of solute atoms on 9R phase stabilization in Al alloys through first-principles calculations. Based on two distribution models of solute atoms, namely, the uniform distribution and the Fermi–Dirac distribution models, we discuss the influences of solute concentrations and finite temperatures on the increments of intrinsic stacking fault energy in the 9R phase structure. The results reveal that high-concentration solute atoms (Ga, Ge, Sc, Si, Sn, Sr, and Y) can promote 9R phase stabilization. Among them, the Sr atom shows the highest performance, but its stabilization can be disrupted by high temperature. These findings serve as a valuable guidance for designing and using high-performance Al alloys with the 9R phase structure.

     

SPS法制备AgSb1-xGaxTe2(x=0~0.2)的微结构和热电性能

采用放电等离子烧结技术(SPS)制备了AgSb1-xGaxTe2 (x=0～0.2),并研究其微结构和热电性能.结果表明:AgSb1-xGaxTe2具有与AgSbTe2相同的晶体结构,并形成了第二相AgGaTe2;掺Ga后,合金的Seebeck系数高于未掺Ga的参照样品AgSbTe2,热导率也低于AgSbTe2;在375 K时,摩尔分数x为0.1的合金AgSb0.9Ga0.1Te2的最大ZT值达到0.29,比AgSbTe2约高0.08.     

Phase relationships and stability of the μ and ζ phases in the ag-a1-x (x = zn,ga, ge) systems

Details of phase relationships in three ternary systems, Ag-Al-X (X = Zn, Ga, Ge), near the Ag-rich corner at 400 °C are presented. Metallography, XRD, scanning electron microscopy, and X-ray spectroscopy have been used to establish the respective isothermal sections at 400 °C. In each case, the μ phase and the ζ phase of the Ag-Al binary system extend into the ternary system and terminate at a three-phase region involving the Ag-rich primary solid solution (α₁ phase) in the Ag-Al-Zn and Ag-Al-Ga systems and the Ge-rich primary solid solution (α₂ phase) in the Ag-Al-Ge ternary system. The stability ranges of the μ and ζ, phases follow approximately constant electron concentration lines. The solid solubilities of Zn, Ga, and Ge in the μ phase are relatively small compared with those in the ζ, phase (up to 18 at.%). No ternary phase appears to exist in the Ag-rich portions studied in the three ternary systems.     

Crystal structures and hydrogenation behavior of （Ca0.9Sr0.08（Al1-xZnx）3 alloys

The crystal structures and hydrogenation behavior of the （Ca0.9Sr0.1）8（Al1-xZnx）3 （x = 0, 0.1, 0.2, 0.3 and 0.4） alloys were investigated. The new phase （Ca,Sr）E（Al,Zn） was found whenx 〉 0.1. （Ca, Sr）E（Al,Zn） crystallizes in space group 14/mmm （A-139）. The lattice parameters were calculated to be a = b = 1.1616（2） nm, c = 1.6422（4） nm. Zn atoms occupy the 8h and 16n sites together with Al atoms. The （Ca0.9Sr0.1）8Al3 alloy only contains a single Ca8Al3 phase. The （Ca0.9Sr0.1）8（Al1-xZnx）3 alloys consist of Ca8Al3, CasZn3, Ca and （Ca,Sr）2（Al,Zn） phases when x is from 0.1 to 0.3. As x increasing to 0.4, the alloy consists of （Ca,Sr）E（Al,Zn）, Ca8Zn3 and Ca. The hydrogenated （Ca0.9Sr0.1）8Al3 and （Ca0.9Sr0.1）8（Al0.9Zn0.1）3 samples consist of CartE and Al. The （Ca0.9Sr0.1）8（Al1-xZnx）3 （x = 0.2, 0.3 and 0.4） samples can be hydrogenated into CaH2, Al and CaZnl3 under a hydrogen pressure of 5 MPa at 473 K.     

First-principles investigation of electronic,mechanical and thermodynamic properties of L12 ordered Co3(M,W) (M = Al,Ge, Ga) phases

Studies were carried out on the equilibrium structural, temperature-dependent mechanical and thermodynamic properties of the Co₃(M, W) (M = Al, Ge, Ga) phases in terms of first-principles calculations. The results of the ground-state elastic constants revealed that Co₃(M, W) phases are mechanically stable and possess intrinsic ductility. It was found that the elastic heat-resistant properties of Co₃(Ge, W) phase are inferior to those of Co₃(Al, W) and Co₃(Ga, W). Analyzing the charge density difference provides the explanation that the sharp decrease in mechanical properties is mainly due to the weakening of Co–Ge bonding at elevated temperatures for Co₃(Ge, W). The elastic anisotropy as a function of temperature is discussed using a universal index. It is observed that Co₃(M, W) phases show a high degree of elastic anisotropy. The degree of elastic anisotropy could be significantly decreased by an increase in temperature for Co₃(M, W). The lattice vibration is treated with the quasiharmonic phonon approach, considering both the vibrational and thermal electronic contributions. The thermodynamic properties as a function of temperature are computed without any adjustable parameters, including heat capacity, entropy, enthalpy and thermal expansion coefficient.     

退火温度对Nd2(FeGaCo)14B/α-Fe纳米复合材料磁性能的影响

用熔体快淬和晶化处理的方法制备了Nd2(FeGaCo)14B／α—Fe纳米复合材料，研究了晶化热处理温度和时间对材料磁性能的影响。结果表明Nd8Fe84.5Ga1Co2B4.5纳米复合材料的磁性能随热处理条件而变化，低温长时间和高温短时间热处理所得样品的最佳磁性能相当。     

添加Sb的Ga2Te3合金热电性能

本研究采用等摩尔分数的Sb元素替换Ga2Te3中的Ga元素,并利用放电等离子烧结技术制备Ga1.9Sb0.1Te3合金,研究其微观结构和热电性能。结果表明,添加Sb元素后,材料的Seebeck系数为130～240μV/K,明显低于单晶Ga2Te3,电导率为3600～1740??1·m?1,至少是单晶Ga2Te3的17倍,热导率提高近25%。在649K时Ga1.9Sb0.1Te3合金的热电优值(ZT)达到最大值0.1,是同温度下单晶Ga2Te3ZT值的3倍。