Magnetic susceptibility studies of (CH2)3(NH3)2FeCl2Br2 and (CH2)6(NH3)2FeCl2Br2

The magnetic susceptibility of the layered compounds (CH₂)₃(NH₃)₂FeCl₂Br₂ and (CH₂)₆(NH₃)₂FeCl₂Br₂ has been measured in the range 80 < T < 300 K. The results follow a Curie-Weiss behavior in the range 120 < T < 300 K but are field dependent for T < 120 K. The results are interpreted in terms of a two-dimensional antiferromagnetic interaction which is canted. A comparison with the corresponding pure chloride compounds is given.     

metamagnetic behavior of linear chain pyridine compounds: Co(Pyridine)2Cl2, Fe(Pyridine)2Cl2, Fe(Pyridine)2(NCS)2 and Ni(Pyridine)2Cl2

Magnetic phase transitions in the pyridine (pyr) compounds Co(pyr)₂Cl₂, Fe(pyr)₂Cl₂, Fe(pyr)₂(NCS)₂ and Ni(pyr)₂Cl₂ have been observed at applied magnetic fields of ～0.7, 0.7, 1.1 and 2.7 kG respectively. These low field phase transitions are observed in the Fe and Ni compounds at T = 4.2 K, and in the Co compound at T < 3K, and are consistent with metamagnetic behavior. Magnetic saturation is not achieved in any of these compounds for fields of 60 kG, reflecting high anisotropy.     

Linear-chain antiferromagnetism in Ni(N2H5)2(SO4)2

The compound dihydrazinium bis(sulfato) niccolate(II), Ni(N₂H₅)₂(SO₄)₂, containing sulfato-bridged chains of Ni(II) ions, can be described as an antiferromagnetic Heisenberg linear-chain system. A reasonable agreement of susceptibility measurements in the temperature region 2–80K, with a theory developed by Weng for antiferromagnetic Heisenberg linear chains with spin S=1, is obtained for a value of the intra-chain interaction $\text{J}\text{k}\text{=?3.35K}$. Preliminary results of specific heat measurements, on the other hand, do not fit quite well using this model. The origin of this discrepancy is suggested to be a zero-field splitting of the single ion.     

Electron paramagnetic resonance of Mn IN (NH4)2Co2(SO4)3 and (NH4)2Ni2(SO4)3 single crystals

EPR studies are reported on single crystals of ammonium cobalt sulphate and ammonium nickel sulphate containing Mn²⁺ ions. In each case only one magnetic complex of Mn²⁺ ion is found. The resonance lines in the case of Mn²⁺ doped ammonium nickle sulphate are characterised by a strong angular dependence of line intensities. The resonance lines in both the cases are fitted to a spin-Hamiltonian corresponding to orthorhombic symmetry.     

Linear-chain ferromagnetism in the one-dimensional compounds CoCl2(pyrazole)2 and CoCl2(indazole)2

Two linear-chain compounds of formula CoCl₂L₂, with L = pyrazole (pz) and indazole (indz), have been investigated with the aid of IR, far-IR, ligand field and ESR spectra. Magnetic susceptibility data have been collected in the temperature region 4.2–80 K. Analysis of the susceptibility data in terms of the Ising model yielded the values of the ferromagnetic intrachain exchange constants J = 7.2(6) and 7.4(9) cm^-1 for the pz and indz compound, with corresponding g-values of g∥ = 7.9(7), g⊥ = 4.6(9) and g∥ = 10.8(9), g⊥ = 3(1), respectively. The results are discussed and compared with the similar compound CoCl₂(pyridine)₂. The influence of the bridge geometry and of the π-bonding properties of the organic ligands on the exchange constant are considered for the explanation of different J-values. It is suggested that the π-bonding properties of the organic ligand influence the magnitude of the superexchange constant to a great extent.     

On the room-temperature ferromagnetism in (ZnO)0.98(MnO2)0.02

Room-temperature ferromagnetism (RTFM) is investigated in the polycrystalline bulk (ZnO)_0.98(MnO₂)_0.02 samples prepared by a modified solid-state sintering route. Successive sintering of a sample was carried out in air at different temperatures in the range of 400-1000 °C. The study of magnetization and phase-investigation in the sample was carried out after each sintering step. The progressive suppression of impurities and the consequent reduction in RTFM is clearly observed in the samples with increase in the sintering temperature up to 800 °C. The subsequent successive sintering of the (ZnO)_0.98(MnO₂)_0.02 sample up to 1000 °C yields fully paramagnetic sample exhibiting wurtzite structure. The studies support the conjecture (Kundaliya et al., Nat. Mater. 3 (2004) 709 [18]) that RTFM in this system has an origin related to a randomly distributed impurity phase produced by local dissolution of ZnO and MnO₂.     

Mg2(BH4)2(NH2)2脱氢机理的理论研究

对Mg₂(BH₄)₂(NH₂)₂的脱氢机理展开系统的理论研究发现相对于分子内的脱氢过程,分子间的脱氢过程在热力学和动力学方面都是比较有利的. Mg₂(BH₄)₂(NH₂)₂脱氢过程的第一步是BH₄^-中的B-H^δ-和NH2-中     

Magneto-optical measurement on the layer type magnet (CH2)2(ND3)2MnCl4

The linear birefringence (LB) of the antiferromagnet (CH₂)₂(ND₃)₂MnCl₄ has been measured as a function of temperature and in magnetic fields up to 100 kOe. The temperature dependence of the LB points to a pronounced two dimensional magnetic behaviour. No anomaly corresponding to the effect of three dimensional ordering could be detected at T_N. In theffield dependent measurements the spin flop at H_SF = 33.6 ± 1 kOe (T = 4K) could clearly be detected.     

Kinetics of the rehydration of Fe(NH4)2(SO4)2. 4H2O

The kinetics of the reaction of ferrous ammonium tetrahydrate with water has been studied at room temperature using the Mössbauer effect. Data were fitted to two equations and from the results it is concluded that the reaction is diffusion controlled.     

Chlorine K X-ray absorption-edge structures of CIS-[Pt(NH3)2Cl2], trans-[Pt(NH3)2Cl2], trans-[Pd(NH3)2Cl2] and (NH4)2PdCl4

The K absorption-edge spectra of the ligand chlorine ion in square-planar complex compounds cis- and trans-[Pt(NH₃)₂Cl₂], trans-[Pd(NH₃)₂Cl₂], and (NH₄)₂PdCl₄ are reported and discussed in connection with the chlorine K absorption spectra of K₂PtCl₄ and K₂PdCl₄, reported previously. The observed chemical shift of a white line at the absorption threshold is interpreted in terms of the difference of the ligand-field splitting of electronic states for metal ions. The white line is attributed to the electronic transition from the Cl^? ls level to the lowest unoccupied antibonding molecular orbital (MO), which is specified by a $\text{MO}\text{b}{}_{\mathrm{1g}}\text{(σ}{}^1\text{)}$ in the square-planar complex with D_4h symmetry. The other absorption structures are regarded as continuum “shape resonances” of the outgoing electron trapped by the cage of the surrounding atoms. The effect of geometrical isomerism is found in the chlorine K absorption spectra of cis- and trans-[Pt(NH₃)₂Cl₂].     

Proton conduction in (NH4)3 H(SO4)2 single crystals

D.C. electrical conductivity, DTA and coulometric studies on (NH₄)₃ H(SO₄)₂ single crystals are made. Conductivity is markedly anisotropic with maximum along c¹ direction. A sudden jump in the conductivity plot along c¹ direction at 413 K is supported by a large endothermic peak in DTA, confirming the presence of transition at this temperature. The values of activation energy calculated from conductivity measurements indicated that the charge carriers are protons. This was further confirmed by coulometric experiment where the gas evolved was hydrogen, as established by a gas chromatograph and the volume of H₂ released agreed with that expected from electrolysis. The mechanism of protonic conduction in this crystal is discussed.     

Structure and electrical conductivity of a novel inorganic solid electrolyte: Na14.5[Al(PO4)2F2]2.5[Ti(PO4)2F2]0.5 (NATP)

A novel inorganic solid electrolyte with a layered framework structure stable up to 1043 K, Na_14.5[Al(PO₄)₂F₂]_2.5[Ti(PO₄)₂F₂]_0.5 (NATP), has been hydrothermally prepared and characterized by single-crystal and powder X-ray diffraction techniques, X-ray fluorescence (XRF) analysis, IR spectroscopic measurement, thermogravimetric and differential thermal analysis (TGA and DTA). NATP crystallizes in the acentric hexagonal space group P3 with a=10.448(2), b=10.448(2), , Z=1, containing a large number of Na⁺ cations in the interlamellar space and the cavities of its framework. There are six different crystallographic Na⁺ cationic sites, in which 8% Na(5) and 12% Na(6) sites are vacant. Electrical conductivity measurements show that Na⁺ cations exhibit a high mobility with two domains for the electrical conductivity versus temperature.     

Nonplanar domain walls in ferroelastic Gd2(MoO4)3 and Pb3(PO4)2

A new stable, mobile zigzag-shaped domain wall configuration has been discovered in the Gd₂(MoO₄)₃ and Pb₃(PO₄)₂ structures. Previous work on these materials had not predicted this type of domain wall. The zigzag walls have mobilities 30–40 times that of planar walls in the same material. This increased mobility can be explained as a geometrical effect.     

Vibrational spectra of (CD3)2Cd and (CD3)2Zn

The Raman and infrared spectra of (CH₃)₂Cd and (CH₃)₂Zn have been reexamined and are reported along with previously unreported vibrational data for (CD₃)₂Cd and (CD₃)₃Zn. The spectra have been analyzed using the double group $\text{G}{}_{36}\text{2}$, which has led to some changes in assignments made previously. Comparison is also made with a recent study of (CH₃)₂Hg and (CD₃)₂Hg. Fine structure was observed for two of the vibrations of the E_1d symmetry species, arising from internal rotation of the methyl groups. This structure has been analyzed using a recently developed theory for molecules of the freely rotating dimethylacetylene type. Problems which arise in the application of this theory have been pointed out, and it is suggested that some additional consideration of the theory may be necessary.     

Synthesis and magnetic properties of Pr(Fe 1-xCo x) 2 and Pr 1-yTb y(Fe 0.4Co 0.6) 2 alloys

Measurement of X-ray diffraction, magnetization and magnetostriction was made on the Pr(Fe_1-xCo_x)₂ (x=0.4, 0.5 and 0.6) and Pr_1-yTb_y(Fe_0.4Co_0.6)₂ (y=0, 0.1, 0.2 and 0.3) alloy series. It was found that a cubic phase with the MgCu₂ structure can be obtained in the Pr(Fe_1-xCo_x)₂ series only at x=0.6. The Pr_1-yTb_y(Fe_0.4Co_0.6)₂ system has the cubic MgCu₂ structure over the studied range for y. The lattice constant and magnetization decrease and the Curie temperature increases with increasing y. At 7 K, Pr_1-yTb_y(Fe_0.4Co_0.6)₂ samples are found to have huge intrinsic coercivities, which are associated with narrow domain walls. It is also found from X-ray measurement that in Pr_1-yTb_y(Fe_0.4Co_0.6)₂ the spontaneous magnetostriction ₁₁₁ increases due to Tb substitution, while the saturation magnetostriction _s is much lower than ₁₁₁. This can be attributed to the large value of ₁₀₀ with an opposite sign to ₁₁₁, which may be caused by the filling of the d band due to Co substitution. PACS 75.80.-g; 61.10.-i; 75.60.-d     

Uniaxial stress measurements on Rb2PbCu(NO2)6 and K2PbCu(NO2)6

EPR measurements on crystals of compressed tetragonal Rb₂PbCu(NO₂)₆ and K₂PbCu(NO₂)₆ subjected to uniaxial stress have been carried out at various temperatures. The results indicate that uniaxial stress can reorient the crystal axes in both compounds and that smaller stresses are required for Rb₂PbCu(NO₂)₆ than for K₂PbCu(NO₂)₆ at comparable temperatures. Larger stresses are required at lower temperatures.     

Dielectric dispersion in the incommensurate phases of [N(CH3)4]2CoCl4 and [N(CH3)4]2ZnCl4

The complex dielectric permittivity ?(ω) of [N(CH₃)₄]₂CoCl₄ and [N(CH₃)₄]₂ZnCl₄ along the a-axis was measured between 0.35 MHz and 100 MHz. It has been found that for both substances the relaxation frequencies are about 5 MHz at T_c. The dielectric relaxation of both substances could be described by a polydispersive process β = 0.74 in the vicinity of T_c. However, for the temperature region of (T?T_c) > 0.6 for [N(CH₃)₄]₂CoCl₄ the dielectric absorption seems to be rather monodispersive.     

Phase transitions in [Ni(NH3)6](NO3)2

Electric permittivity ^* = ′ − i″ of nickel-hexammino nitrate (NHN) has been measured within the range of temperature from 9 to 300 K at a frequency of 8.8 GHz (X-band). It has been found that the phase transitions at T_k1 = 247 K and T_k2 = 90 K are discontinuous structural transitions between centrosymmetric phases, whereas the transition at T_c = 63 K is a continuous phase transition (glass?).     

Photocatalytic Activity of N-doped TiO2 Photocatalysts Prepared from the Molecular Precursor (NH4)2TiO(C2O4)2

用不同温度控制分解草酸氧钛铵制备N掺杂TiO₂光催化剂．利用XRD、IR、热分析、N₂吸-脱附等温线、XPS、紫外可见漫反射光谱和SEM表征了N-TiO₂光催化剂的结构．400～600 oC焙烧的N-TiO₂光催化剂为纯锐钛矿相,而700 oC焙烧的N-TiO₂光催化剂为锐钛矿和金红石混合相．N掺杂在TiO₂的间隙位使锐钛矿相TiO₂带隙变窄．在光降解甲基橙的反应中,600和400 oC焙烧的N-TiO₂催化剂分别在紫外光和全波长光照射下有最好活性;700 oC焙烧的N-TiO₂催化剂无论在紫外光和全波长光下都表现出最好的比活性,即最高的光量子效率,这可以归因于700 oC焙烧的N-TiO₂光催化剂良好的结晶程度和锐钛矿-金红石异相结的存在．     

Thermoelectric power of TTF[Ni(dmit)2]2

The 1D organic salt TTF[Ni(dmit)₂]₂ becomes superconductor with T_c=1.6 K under an applied hydrostatic pressure of 7 kbar. Structural determinations in this system lead us to suspect that superconductivity (SC) coexists with a charge density wave (CDW) instability at low pressure. In order to better understand how SC emerge from a CDW and to revisit the pressure–temperature phase diagram of the TTF[Ni(dmit)₂]₂ we performed transport and thermoelectric power measurements under pressure.