Mossbauer and magnetic studies on the system Fe3−x Ti x O4

Mossbauer measurements have been made on the system Fe_3?x Ti _x O₄ for 1·0 ≥x ≥ 0. This system is interesting in that it is expected to form a continuous solid solution over the whole range and also occurs naturally. Spectra taken at various temperatures between 300 K and 77 K show complex behaviour. The results can be understood in terms of disorder and consequent formation of superparamagnetic clusters which are supported by our earlier hysteresis and susceptibility studies at various temperatures. It appears that with increasing Ti content domain wall formation is inhibited resulting in effectively monodomain clusters. Considering the work reported by others, we suggest that Mossbauer spectra of multidomain material should show well-resolved magnetic hyperfine spectrum, even close to itsT _N .     

Investigation of structural transport and magnetic properties of the system Li0.25Cu0.5Fe2.25- x Al x O4

Experimental data on X-ray electrical conductivity, thermoelectric coefficient, magnetic hysteresis and infrared absorption spectra of the system Li_0.25Cu_0.5Fe_2.25–x Al _x O₄ are presented. All the compounds, 0x2.25, showed cubic symmetry. Lattice constant values progressively decreased on increasing the Al³⁺ content. X-ray intensity calculations, magnetic hysteresis and infrared spectroscopy studies indicated the presence of Li⁺, Al³⁺ and Fe³⁺ at tetrahedral and octahedral sites, while Cu²⁺ is present only at the octahedral site. The activation energy and threshold frequency increased with increasing values ofx. The compounds withx1.50 aren-type, and those withx2.0 arep-type semiconductors. Magnetic hysteresis indicated that compounds withx1.50 are ferrimagnetic, and those withx2.0 are antiferrimagnetic. High coercive force,H _c, values and remanence ratios (J _R/J_S) showed that all the compounds exceptx2.0 exhibit single-domain behaviour. The probable ionic configuration for the system is suggested as Li _0.15 ⁺ Al _0.5 ³⁺ Fe _0.35 ³⁺ [Li _0.1 ⁺ Cu _0.5 ²⁺ Fe _0.4 ³⁺ Al³⁺]O ₄ ^2– .     

Synthesis and structural studies on Ni0.5+x Zn0.5Cu x Fe2−2x O4

The mixed ferrites of Ni–Zn–Cu are synthesized using ceramic double sintering technique. Cu and Ni are substituted in steps of x=0.1 at the interstitial sites of Fe. Powders of mixed ferrites of Ni–Zn–Cu are studied using XRD. The mixed ferrites show a single phase and face center cubic structure for all concentrations. The substitution of Cu and Ni are confirmed from the variation of lattice constant. The cation distribution in the A and B sites of the ferrites is estimated. Mixed ferrites of Ni–Zn–Cu are characterized using a.c. conductivity and magnetic susceptibility methods. The variation of activation energy, magnetic moment and Curie temperature with concentration of Fe ions explains the alterations of the energy levels of d bands. Hopping of charge carriers and the presence of different ionic states of Ni, Cu, and Fe ions are discussed using the FTIR and EPR spectra.     

Preparation, electrical conductivity, and magnetic susceptibility of (Ba1 − x Bi x )(Mn0.5 + x/2Nb0.5 − x/2)O3

(Ba_{1 ? x} Bi _x )(Mn_{0.5 + x/2}Nb_{0.5 ? x/2})O₃ perovskite solid solutions have been prepared by solid-state reactions and their physicochemical properties have been investigated. We have studied the influence of bismuth substitution for barium cations on the phase composition of the samples. Their magnetic susceptibility and electrical conductivity have been measured as functions of temperature. The composition dependence of the antiferromagnetic ordering temperature is presented.     

Synthesis, Structural, Electrical and Magnetic Characterization of Mn0.5Mg0.5?x Ni x Fe2O4 Spinel Nanoferrites

Nanoferrites of composition Mn_0.50Mg_0.5?x Ni _x Fe₂O₄ with 0.00??x??0.50 were prepared by the chemical coprecipitation method. The prepared nanoferrites were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), atomic force microscopy(AFM), dc electric resistivity and magnetic properties using vibrating sample magnetometer (VSM) to study the structural, morphological, electrical, and magnetic changes taking place with varying Ni and Mg concentration in the composition of the prepared nanoferrites. The XRD results indicated the formation of single spinel ferrite with crystalline size in the range of 16?C24?nm. The lattice parameter (a) decreased with the decrease of the Mg concentration. IR reveals the presence of both high and low frequency bands due to tetrahedral and octahedral sites, respectively. Further information about the morphology of the nanoferrites was obtained from AFM and SEM measurements. Electrical properties indicate that synthesized samples have high resistivity. The magnetic hysteresis curves clearly indicate the soft nature of the prepared nanoferrites. Various magnetic parameters such as saturation magnetization (M _s ), and remanence (M _r ) are obtained from the hysteresis loops and observed to be dependent on the composition.     

溶胶凝胶法制备Li4.5B0.5Si0.5O4-xLi2O导体材料及导电性能

采用溶胶－凝胶法制备了Ｌｉ４．５Ｂ ０．５Ｓｉ０．５Ｏ４－ｘＬｉ２Ｏ（ｘ＝０～０．５）离子导体材料,并采用ＤＴＡ－ＴＧ、ＸＲＤ、ＴＥＭ及交流阻抗等技术对样品进行了分析和测试,结果发现：溶胶－凝胶法可降低Ｌｉ４．５Ｂ０．５Ｓｉ０．５Ｏ４的合成温度;随Ｌｉ２Ｏ的掺入可增强基质材料的致密性并提高其离子的导电性能。     

Synthesis, structure, dielectric properties, and electrical conductivity of (La0.2Sr1.8)[Ga(Fe1−x Mgx)]O5.1−x/2 solid solutions

(La_0.2Sr_1.8)[Ga(Fe_1?x Mg_x)]O_5.1?x/2 oxygen-ion conducting ceramics have been prepared by solidstate reactions. The cation substitutions have been shown to give rise to lattice expansion, accompanied by a reduction in electronic conductivity and a rise in ionic conductivity owing to the increase in the concentration of oxygen vacancies upon a reduction in transition-metal content.     

Quantitative analysis of a Fe3O4 + Li x Fe3O4 sample by the X-ray Rietveld method

The Li _x Fe₃O₄ phase shows a strong peak-overlapping with those of pure magnetite, and a routine X-ray analysis does not allow the detection of the presence of any Fe₃O₄. However, a careful inspection of the observed calculated difference pattern has led to the deduction of the presence of Fe₃O₄. This paper shows that the Rietveld method can be used to obtain significant information about the relative concentration of the components of a two-phase sample, even in the case of poor crystallinity, strong overlapping between the diffraction peaks, and only a partially known structure.     

Characterization of La1 −x Sr1 +x Cu5 −x Fe x O12 + δ (0 ≤x ≤ 1·0) by dc electrical conductivity,magnetic susceptibility and EPR measurements(0 ≤x ≤ 1·0) by dc electrical conductivity,magnetic susceptibility and EPR measurements

The DC electrical resistivity results of La_{4 −x} Sr_{1 +x} Cu_{5 −x} Fe _x O_{12 + δ} (0 ≤x ≤ 1·0) showed that for S1 (x = 0) and S2 (x = 0·25) the temperature coefficient of resistivity (TCR), dρ/dT, is positive and slightly increases with increasing temperature in the range 20–270 K. This shows the metallic nature of S1 and S2. For the samples S3(x = 0·5) and S4 (x = 0·75), TCR slightly increases in the range 20–270 K, with change in sign from negative to positive at ∼ 80 K and ∼ 130 K, respectively. These results show the metal-insulator type transition in S3 and S4. For the sample S5 (x = 1·0), the TCR is negative and gradually increases in the range 20–270 K, which shows its semiconductor-like behaviour. The activation energy for S5 is found to be 0·21 × 10⁻² eV. Furthermore, the DC resistivity results of S1–S5 in the range 350–660 K are in conformity with the low temperature results. The very weak temperature dependence of magnetic susceptibility results of S1–S3 show Pauli-paramagnetic behaviour in the range 77K–400 K, while S4 and S5 exhibit Pauli-paramagnetic behaviour in the range 77–850 K. Long-range antiferromagnetic interaction is observed in S5 (x = 1·0) belowT _c ∼ 100 K. The room temperature EPR lineshapes gradually improve from metallic S1 (x = 0) to semiconductor-like S5(x = 1·0). Negativeg-shift is observed in the samples S2–S5 with increasing trend ing _iso-values of 1·880 in S2 to 1·961 in S5. However, theg _iso-value for S1 could not be observed due to very poor lineshape.     

Lattice disorder and electrical conductivity of flux-grown Ca(WO4) x (MoO4)1−x crystals

The growth of solid solutions of Ca(WO₄) _x (MoO₄)_1–x in the rangeX=0.072 to 0.86 has been successfully accomplished for the first time, employing a flux technique. The fact that proper mixing occurs is established by observing the variation in unit cell parameters and density of the crystals. The electrical conductivity of the pelletized samples is interpreted in terms of Schottky and Frenkel defect concentrations. The role of oxygen ion vacancies is stressed for the intrinsic region of conductivity.     

Dielectric properties of the system Pb2-x La x Li0.5 O6 + δ

The dielectric properties of the ceramic pyrochlore structured system Pb_2-x La _x Li_0.5Nb_1.5 O_{6 + δ} has been studied as a function of concentrationx and frequency at room temperature 25°C. The results have been analysed for relaxation process and conduction mechanism.     

Microwave-induced combustion synthesis of Li0.5Fe2.5−xCrxO4 powder and their characterization

Li_0.5Fe_2.5−xCr_xO₄ (0 ≦ x ≦ 1.0) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion, using lithium nitrate, iron nitrate, chromium nitrate, and carbohydrazide as the starting materials. The process takes only a few minutes to obtain as-received Cr-substituted lithium ferrite powders. The resultant powders annealed at 650 °C for 2 h and were investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermomagnetic analysis (TMA). The results revealed that the lattice constant decreases linearly with increasing of Cr content in Li_0.5Fe_2.5−xCr_xO₄ specimens. Moreover, the magnetic properties of Cr-substituted lithium ferrite were also strongly affected by Cr content. The saturation magnetization, remanent magnetization, and coercive force decrease monotonously with increasing of Cr content.     

Ionic conductivity of the Na1+xM x III Zr2−x(PO4)3 systems (M = Al,Ga, Cr,Fe, Sc,In, Y,Yb)

The existence and ionic conductivity of solid solutions Na_1+xM _x ^III Zr_2–x(PO₄)₃ with Nasicon-like structure have been investigated and the results compared with literature data. A limited range of solid solutions is formed with M^III = aluminium, gallium, yttrium, ytterbium, whereas a continuous series is obtained for M^III = chromium, iron, scandium, indium. The pure end member Na₃ln₂(PO₄)₃ is reported for the first time; according to powder diffraction data, it is hexagonal witha = 0.8966(1) andc = 2.2104(4) nm. The small monoclinic distortion already known for M^III = chromium, iron and scandium is restricted tox values very close to 2. Ionic conductivity measurements show that for a given value ofx, the mobility of the Na⁺ ions is strongly influenced both by the ionic radius and the type of electronic structure of the M^III ion. However, no simple correlation can be found.     

Mössbauer spectroscopic studies of Y3−x Gd x Fe5O12(x =0, 0.5 and 3.0) prepared by an amorphous citrate process

The system Y_3-x Gd _x Fe₅O₁₂(x = 0, 0.5 and 3.0) synthesized through an amorphous citrate gel process has been investigated by Mössbauer and EPR spectroscopy. These studies delineate the co-ordination, symmetry, valence and relaxation phenomena which in turn give information on the growth of garnet and other phases in the above system. Furthermore these studies help in finding the optimum growth conditions for the garnet phase.