Crystal structures and magnetic properties of iron (III)-based phosphates: Na4NiFe(PO4)3 and Na2Ni2Fe(PO4)3

Crystal structures from two new phosphates Na₄NiFe(PO₄)₃ (I) and Na₂Ni₂Fe(PO₄)₃ (II) have been determined by single crystal X-ray diffraction analysis. Compound (I) crystallizes in a rhombohedral system (S. G: R-3c, Z = 6, a = 8.7350(9) Å, c = 21.643(4) Å, R₁ = 0.041, wR₂=0.120). Compound (II) crystallizes in a monoclinic system (S. G: C2/c, Z = 4, a = 11.729(7) Å, b = 12.433(5) Å, c = 6.431(2) Å, β = 113.66(4)°, R₁ = 0.043, wR₂=0.111). The three-dimensional structure of (I) is closely related to the Nasicon structural type, consisting of corner sharing [(Ni/Fe)O₆] octahedra and [PO₄] tetrahedra forming [NiFe(PO₄)₃]⁴⁺ units which align in chains along the c-axis. The Na⁺ cations fill up trigonal antiprismatic sites within these chains. The crystal structure of (II) belongs to the alluaudite type. Its open framework results from [Ni₂O₁₀] units of edge-sharing [NiO₆] octahedra, which alternate with [FeO₆] octahedra that form infinite chains. Coordination of these chains yields two distinct tunnels in which site Na⁺.The magnetization data of compound (I) reveal antiferromagnetic (AFM) interactions by the onset of deviations from a Curie-Weiss behaviour at low temperature as confirmed by Mössbauer measurements performed at 4.2 K. The corresponding temperature dependence of the reciprocal susceptibility χ⁻¹ follows a typical Curie-Weiss behaviour for T > 105 K. A canted AFM state is proposed for compound (II) below 46 K with a field-induced magnetic transition at H ≈ 19 kOe, revealed in the hysteresis loop measured at 5 K. This transition is most probably associated with a spin-flop transition.     

The effect of oxygen vacancies on the structure and electrochemistry of LiTi2(PO4)3 for lithium-ion batteries: A combined experimental and theoretical study

We report that a partially oxygen deficient LiTi₂(PO₄)₃ shows a much better rate capability as a cathode material for lithium-ion batteries compared to stoichiometric LiTi₂(PO₄)₃. A combination of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electrochemistry, and first-principles calculations was used to determine and rationalize the structural and electrical changes that occur with different heat treatment atmospheres. XRD and XPS experiments confirmed that some Ti⁴⁺ transformed to Ti³⁺ in oxygen deficient LiTi₂(PO₄)₃ heat treated under N₂; Ti³⁺ was detected and the lattice parameter increased compared to that of LiTi₂(PO₄)₃. Electrical conductivity measurements indicated an increase in the electronic conductivity of nearly two orders of magnitude for the oxygen deficient LiTi₂(PO₄)₃ sample compared to LiTi₂(PO₄)₃. First-principles calculations suggest that the oxygen vacancies could be formed in LiTi₂(PO₄)₃ under oxygen-poor conditions, and this may significantly decrease the donor levels of other possible donor defects and thus improve the electronic mobility.     

快离子导体Na2＋xZr2—xYbxSiP2O12系统的研究

以高温固相反应制备了 Na_(2 x)Zr_(2-x)Yb_xSiP_2O_(12)系统的合成物,确定了它们的相组成以及 Nasicon 单纯相的范围。计算了系统合成物的晶胞参数,测定了它们从室温至400℃的电导率。x=1.5的合成物具有最好的导电性,在300℃时其电导率为3.65×10~(-2)(Ω·cm)(-1),在200～400℃温区内其活化能为26.36 kJ/mol。     

Na_3Hf_(2-x)TixSi_2PO_(12)系统快离子导体的研究

以 Na_3PO_4、HfO_2、SiO_2为主要原料,铂舟为反应器皿,在900～1200℃的高温下,加热数小时至20h(少数样品达40h),合成了一系列合成物。多数反应在1100～1150℃进行。x=0～0.5的合成物为 NASICON和 HfO_2的二相区。x=0.6～1.0时为 NASICON 单纯相。x>1.0开始出现玻璃态。系统合成物的电导性测定结果发现除母体以外最好的是 x=0.6的合成物。其电导率在400℃时为2.76×10~(-2)(Ω·cm)~(-1)。它的活化能在200～400℃温区里为25.5kJ/mol。     

Nasicon材料的制备及气敏特性研究

采用高温固相烧结方法,制备了Ｎａｓｉｃｏｎ固体电解质材料,并用ＩＲ、ＸＲＤ等手段对材料的组成和物相结构进行了表征。在材料电阻率随温度变化的测试结果基础上,进上步以所合成的Ｎａｓｉｃｏｎ材料作离子导体、ＢａＣＯ３－Ｌｉ２ＣＯ３复合盐作第三电极材料制成ＣＯ２传感器,考察了材料的气敏性能。结果表明材料对ＣＯ２具有良好的气敏特性及抗水蒸汽干扰性能。     

Positron annihilation studies on nasicon analogues containing cation vacancies

Positron annihilation studies were carried out on the Nasicon analogue Na₂(La, Al)Zr(PO₄)₃ compound for three different concentrations (2·2, 2·8 and 5·2 by wt.%) of ZrO₂ in the nutrient. Angular correlation study of annihilated photons reveals that the defect concentration is maximum for 2·8 (wt.%) of ZrO₂. Further, positron lifetime studies indicate that the positrons are trapped at cation vacancies. Application of a two-state trapping model to this system made it possible to evaluate the lifetime of positrons in the Bloch state and of positrons trapped at cation vacancies.     

快离子陶瓷晶界阻抗的分布模型

以电导率分布模型为基础的模拟计算可以解释快离子陶瓷晶界部分的非理想阻抗谱。讨论了几率函数的分布参数对阻抗图形的影响。对 Nasicon 陶瓷晶界阻抗谱进行了拟合计算和确定出电阻分布性质。     

二价离子替代的Nasicon及其应用研究

含二价阳离子的Ｎａｓｉｃｏｎ，Ｍ￣（２＋）Ｎａｓｉｃｏｎ（Ｍ＝Ｍｇ、Ｃａ、Ｓｒ、Ｚｎ）可由母体Ｎａ＿３Ｚｒ＿２Ｓｉ＿２ＰＯ＿（１２）（Ｎａｓｉｃｏｎ）为起始原料与相应的二价离子的盐浓液或熔盐进行离子交换而制得。Ｘ射线衍射分析结果表明离子交换后的产物Ｍ￣（２＋）－Ｎａｓｉｃｏｎ大多保持原母体的Ｃ＿（２／ｃ）结构。交流阻抗技术测定的电导率数据显示含不同的二价替代离子的Ｎａｓｉｃｏｎ的电导率相差甚大。其中最好的是Ｍｇ￣（２＋）－Ｎａｓｉｃｏｎ，其电导率在４００℃时可达到１．４８×１０￣（－２）Ｓ／ｃｍ。Ｍｇ￣（２＋）－Ｎａｓｉｃｏｎ用作微功率固态电池Ｍｇ／ＣｕＣｌ的电解质，该电池的开路电压为２．０７Ｖ，短路电流为１ｍＡ。平均放电电压为１．６Ｖ，电池的放电容量是３．４ｍＡＨ。     

Synthesis and Characterization of Li1＋2x＋3y AlxScyZny Ti2-x-2ySixP3-xO12

Recentyearssomenaturalaluminosilicates ,suchaspyrophylliteandkaolinite ,havebeenusedasastartingmaterialstopreparemineralfastionconduc tors .Meanwhile ,somerareearthelementshavebeenintroducedintomineralfastionconductorsystemtoformsocalledrareearthmineralfastionconductors .Intheareaoffastionconductors ,moreandmoreat tentionhasbeenpaidtolithiumfastionconductorsduetotheirpotentialapplicationinhighenergydensi tybatteryandotherelectrochemicaldevices .Severalcomplexesareknowntoshowhighlithiumioncondu…