Nanocrystalline Samples Research Articles

Structure, magnetic and dielectric properties in nano-crystalline Yb[formula omitted]CoMnO[formula omitted

Structural, magnetic and dielectric properties have been studied for Yb2CoMnO6. Nano-crystalline sample of Yb2CoMnO6 synthesized by sol–gel method and structural analysis shows that the sample crystallizes in monoclinic crystal structure with P21/n phase group. To understand the charge state of Co, Mn and Yb we have performed the XPS study. Magnetic study shows that the sample undergoes a paramagnetic to ferromagnetic phase transition around Tc∼56 K and an additional magnetic ordering at a lower temperature around 14 K due to ordering of Yb3+ magnetic ions. Temperature dependent Raman study reveals that spin–phonon interaction is present in this material. Further, we have studied the dielectric properties of this material. We observed that the material shows a relaxation behavior that obeys the thermally activated relaxation mechanism. Impedance spectroscopy reveals that the material shows non-Debye’s behavior. AC conductivity study is performed to understand the conduction mechanics which involve the quantum mechanical tunneling phenomenon.

Study of magnetic and magneto-transport properties of nanocrystalline [formula omitted][formula omitted][formula omitted] compound: Observation of large magnetoresistance

Magnetic and magneto-transport properties of nanocrystalline Nd0.5Ca0.5MnO3 compound are presented. In contrast to its bulk counterparts, with modification of the magnetic grounds state, large magnetoresistance appeared in the presence of comparatively lower magnetic field in nanocrystalline compound. Additionally, the magnetic field induced insulator-metal transition took place in nanocrystalline compound with negligible thermal hysteresis. From application perspectives, observation of the low field magnetoresistance in this compound may be important for several uses in magnetic field sensor related technology. Fundamentally, the influences of the ferromagnetic phase fraction as well as the induced ferromagnetic interaction in nanocrystalline samples on magnetic and magneto-transport properties were addressed.

High Temperature Dielectric Response and AC Conductivity Mechanism of (Nd, Ni) codoped BiFeO3

BiFeO3(BFO)and Bi0.9Nd0.1Fe0.9Ni0.1O3 (BNFNO) nanocrystalline samples have been synthesized through the sol-gel auto combustion process. Frequency and temperature dependent dielectric measurements have been performed in order to apprehend the influence of (Nd,Ni) co-doping on the conduction mechanism of pristine BFO.Thereal part of the dielectric constant is found to increase with the Nd and Ni doping, which is accredited to higher space charge polarization induced by the dopant ions.The dielectric constant measured as a function of frequency exhibits a dispersivebehaviour within low frequency region and attains a constant value at higher frequencies. A thermally activated relaxation peak is found at around 500K in the BNFNO samplewhich shifts towards lower temperatures at higher frequencies. The AC conductivity follows the Jonscher’s universal dynamic law, which has been utilized to evaluate the value of frequency exponent ‘s’. The decrease in the value of the ‘s’ parameter with the increase in temperature establishes that the conduction mechanism is governed by the correlated barrier hopping (CBH) model. The ac conductivity data has been utilized to evaluate the minimum hopping distance (Rmin) and the binding energies (Wm) of the electrons in BNFNO. Arrhenius equation has been used to fit the experimental data and activation energy has been evaluated at different temperatures. The Activation energy is found to increase with the increase in the temperatures, owing to the creation of more oxygen vacancies instigated by (Nd, Ni) co-doping.

Crystallographic inversion-mediated superparamagnetic relaxation in Zn-ferrite nanocrystals

Crystallographic inversion induced shift of resonance frequency in zinc ferrite nanoparticle (ZF-NP) samples is studied here. ZF-NP samples were synthesized by a solution-based, low-temperature (<200 °C), microwave-assisted solvothermal (MAS) process. Owing to the far-from-equilibrium processing condition, the MAS process produces a very high degree of crystallographic inversion, δ=0.61, in the as-synthesized nanocrystallites. A rapid thermal annealing (RTA) technique was adopted to tune-down crystallographic inversion without altering the crystallite sizes in annealed samples. The crystal structures, particle shapes, and compositions of the nanocrystalline samples were characterized by XRD, SEM and Raman spectroscopy. The samples are phase-pure, with particle size in the range 8-16 nm and their compositions are stoichiometrically accurate. The resonance phenomena in 1 to 10 GHz frequency range was measured by analyzing the impedance mismatch of a microstrip line with the magnetic material loaded on to it. The RTA protocol enables tuning of the resonance phenomena in the ZF-NC samples above 6 GHz with tunable range of ∼500 MHz

Зарождение и развитие пластичности в нанокристаллическом ОЦК-железе при сдвиговом нагружении

The features of the nucleation and development of plasticity in nanocrystalline iron with BCC lattice under shear were studied. The mechanisms of plastic deformation playing the main role in the development of structural rearrangements during loading were revealed. It was shown that the development of plasticity can be conditionally divided into several stages. The first stage of plasticity development is associated with the formation and propagation of dislocations and twins. At the second stage, intraganular slip and intergranular sliding begin to make the main contribution to plastic deformation. These processes initiate a change in the shape of the grains. At large shear, the deformation behavior of the sample is governed by the migration of the interfaces. Not only grain boundaries migrate but also twin ones do. As a result of migration processes, the grain sizes of the nanocrystalline sample are enlarged.

Synthesis of a heterojunction CoTiO3/Co3O4 nano-composite thin film with superior photocatalytic activity and reusability: Effect of calcination temperature on phase transformation and effect of oxidants on enhanced degradation of Indo Light Blue dye.

CoTiO3/Co3O4 heterojunction nano-composite was grown by a coprecipitation method at low temperature. The effects of calcination temperature on the phase composition, crystallization and morphology of the cobalt titanates were also examined. Notably, the novel nano-crystalline cobalt titanate with a narrow band gap to coulpe with cobalt oxide (Co3O4) by a direct coprecipitation method (CoTiO3/Co3O4) was attained. The Nano-crystalline samples were systematically characterized by TG/DTG, XRD, DRS, FESEM, FT-IR, EDX and XPS techniques. The results showed that CoTiO3/Co3O4 nano-composite hetero-junction was formed at 650°C, while at 750°C a single phase CoTiO3 nano-crystal was prepared. Photocatalytic activities indicated the heterostructured CoTiO3/Co3O4 nano-composite exhibited much higher photocatalytic activity for degradation of Indo Light blue under visible light irradiation with added oxidants (K2S2O8, KBrO3, and H2O2). The charge separation of CoTiO3 and Co3O4 would result the enhanced visible-light harvesting ability and longer lifetime of photogenerated charge carriers. The stability and reusability of catalysts during four successive cycles were resulted. Finally, a possible mechanism responsible for the charge separation and improved photocatalytic activity was proposed.

Effect of Al3+substitution on the electrical and magnetic properties of Li-base ferrites

Aluminum substituted lithium ferrites with chemical formula Li0.6 (Ni Co)0.2Alx Fe2.2−x O4 (x = 0.0 ,0.15,0.3,0.45,0.6) have been synthesized by sol-gel method and sintered at 900 °C for 5 h. The samples were characterized by XRD, electrical, dielectric and VSM measurements. X-ray diffraction studies confirmed that all the samples exhibit single phase cubic spinel structure with space group Fd3m. The crystallite size, bond lengths, x-ray density and lattice parameters decrease with the increase of Al3+ concentration. Dielectric properties such as dielectric constant (ε′), complex dielectric constant (ε″), tangent loss (tanδ) and ac conductivity (σac) of all the samples were measured and evaluated as a function of frequency at room temperature. The variation of dielectric properties; ε′, ε″, tan and σac versus frequency reveals that the dispersion is due to Maxwell–Wagner type of interfacial polarization in general and the hopping of charge between Fe2+ and Fe3+. The Al-doped nano-crystalline lithium ferrite samples exhibit a very large value of dielectric constant of the order of 104. The room temperature resistivity and activation energy increases with the increase of Al3+ concentration. The temperature dependent resistivity of all samples decreases with increase of temperature indicating the semiconducting behavior. The room temperature DC resistivity increases from 1.65 × 1010 to 2.23 × 1011 ohm-cm. The small value of magnetization may be due to canting superparamagnetic spins at the surface of the samples. The decrease in the magnitude of magnetization value may also be due to the presence of Al3+ paramagnetic ions with spin-down orientation instead of Fe3+ cations with spin-up orientation in the octahedral sites. The squareness ratio (Mr/Ms) is less than 1 which indicates single domain behavior. The increase in coercivity is attributed to lattice defects and decrease is associated with the superparamagnetic behavior.

Study of hydrogen redistribution in Ti49.1Ni50.9 alloy (at %) with nanocrystalline structure by resistometric and durometer methods

The electrolytical hydrogenation of TiNi-based alloys with shape memory and super elasticity results in a significant (by 1,5 times) increase in the microhardness of the surface layer. It is shown that the change of microhardness at long-term aging at room temperature in wire samples of Ti50,1Ni50,9 (at %) alloy with nanocrystalline structure can be used for estimation of diffusion mobility of hydrogen. On wire samples with different diameters it is shown that the increase in the relative electrical resistance at 83K at long-term aging at room temperature for this alloy is also associated with the diffusion mobility of hydrogen. Estimates of the hydrogen diffusion coefficient DH show that in nanocrystalline samples Ti50,1Ni50,9 (at %) the diffusion mobility of hydrogen is higher than in coarse-grained samples. This is connected with the increased contribution of grain boundary hydrogen diffusion in samples with nanocrystalline structure.

Effect of Cu substitution on structural and electric transport properties of Ni-Cd nanoferrites

Nanocrystalline samples of Ni0.7−xCuxCd0.3Fe2O4 (x = 0.0–0.5, with step of 0.1) have been synthesized via auto-combusted sol-gel method. In this study, we present the structural and electric properties of Cu substituted Ni-Cd ferrite nanoparticles at room temperature with varying frequencies from 20 Hz to 15 MHz. X-ray diffraction (XRD) patterns of samples confirm the single-phase cubic spinel structure without impurity. The crystallite size of samples is found in the nano-scale range (17–27 nm) and the lattice parameter is found to increase linearly with Cu content. The surface morphology of samples is studied through a Field Emission Scanning Electron Microscopy (FESEM) and the presence of elements in the samples are confirmed by Energy Dispersive X-ray (EDX) techniques. The materials show dielectric dispersion up to 10 kHz frequencies and their loss tangent values remain very low at MHz frequencies. The impedance and modulus spectroscopy confirm the existence of non-Debye relaxation phenomena of the materials and resolve the contribution of grain and grain boundary. The ac conductivity shows normal behavior with frequency, which is explained on the basis of hopping mechanism.

A prolonged evaluation of air contamination level with CO2 in a college student’s laboratory using nanosized MgO

Three nanocrystalline eco-friendly MgO samples, as pure and modified with 1% (wt/wt) F− or K2O at 600 °C, with high surface area and mesoporous nature were prepared by a simple sonochemical process. The three samples were characterized by XRD, surface area, porosity and TEM techniques. These samples were kept in contact with the atmosphere in the middle of a student’s organic chemistry laboratory and were examined toward capturing the ambient CO2 molecules through continuous exposure for a period of 8 weeks. The capturing capacity of these samples was shown to be in the following order: MgO > MgO-1%F > MgO-1%K2O. After 8 weeks, the amount captured by MgO was 346.2 $$ {\text{mg}}_{{{\text{CO}}_{2} }} \,{\text{g}}^{ - 1} $$, while MgO-1%F captured 311.4 $$ {\text{mg}}_{{{\text{CO}}_{2} }} \,{\text{g}}^{ - 1} $$, and finally MgO-1%K2O had the lowest capturing capacity of 252.9 $$ {\text{mg}}_{{{\text{CO}}_{2} }} \,{\text{g}}^{ - 1} $$. The obtained results showed that our samples are characterized by prolonged activity and reactivity toward the capturing of ambient CO2 molecules. Another series of experiments were carried out by passing pure CO2 gas (instead of the atmospheric CO2) over such samples, inside a glass cubic chamber, for 1 week. The results showed a similar trend in the TG desorption and TPD curves of pure CO2 as those recorded in ambient atmosphere. Values of the molar enthalpy change (ΔH) for CO2 desorption, corresponding to the two steps recorded for each sample in all durations, were calculated and were in agreement with those published formerly. Deconvolution of the IR-broad band, between 1800 and 1200 cm−1, revealed the presence of different types of basic sites on the surface of these samples under investigation.

Optical and magnetic properties of wollastonite and its nanocomposite crystalline structure with hematite

It is important to develop novel, highly bioactive implants with suitable magnetic properties. Nanostructure wollastonites (calcium silicate) with various concentrations of hematite (Fe2O3) up to7% prepared by wet precipitation method and sintered up to (1273 K) were investigated. The developed phases were CaSiO3 of a monoclinic nanocrystalline structure and samples with Fe2O3 contents had both major monoclinic and minor rhombohedral nanocomposite. All samples were in the nano-size based on the XRD data, which was confirmed by HR-TEM analysis and FE-SEM micrographs. The optical diffused reflection spectra were measured at ambient atmosphere (300 K) as a function of wavelength. Optical properties exhibited semiconductor behavior with optical energy band gap of about 2.2 ± 0.07 eV, as a result of the presence of hematite, and the preparation conditions. Magnetic results showed different types of hysteresis at 300 K. Diamagnetic and paramagnetic behavior were observed for wollastonite and its nanocomposite of 1% hematite, while weak ferromagnetic behavior was elucidated for that with 3% hematite. Moreover, butterfly-shape with a bottleneck effect was predominant for nanocomposite of 5% and 7% hematite. The 7% hematite sample has higher values of magnetic parameters rather than the 5% one. The multifaceted magnetic behaviors are due to the Fe2O3 content. Coincided curves of zero field cooling (ZFC) and field cooling (FC) for the 7% hematite sample were verified in temperature range from 100 to 350 K. Advanced Fe2O3-wollastonite containing magnetic properties have triggered attention due to their possible application in bone filler and hyperthermia treatment.

Synthesis, thermal, structural and electrical properties of vanadium-doped lithium-manganese-borate glass and nanocomposites

A glassy sample with a nominal formula LiMn1 − 3x/2VxBO3 (where x = 0.05) was synthesised using the melt-quenching method. Material was characterised by differential thermal analysis (DTA), X-ray diffactometry (XRD) at room temperature and as a function of temperature (HT-XRD), X-ray photoelectron spectroscopy (XPS), impedance spectroscopy (IS) and scanning electron microscopy (SEM). Dependences of glass transition and crystallisation temperatures on the heating rate in DTA experiments were determined. The initial value of electrical conductivity of the glass was 1.4 × 10− 15 Scm− 1. It was significantly increased by a proper thermal nanocrystallisation. The maximum value was higher by 6 orders of magnitude and reached 2.6 × 10− 9 Scm− 1 at room temperature. Expected crystalline phases (i.e. monoclinic and hexagonal LiMnBO3) upon heating were identified and assigned to thermal events observed with DTA. Microstructure of nanocrystalline samples observed by SEM revealed nanocrystalline grains noticeably smaller than 100 nm. Results explaining nanocrystallisation process are coherent.

Study of the dependence of the structural defects and bulk inhomogeneities of nanocrystalline hydroxyapatite on the conditions of production using a biological source of calcium

The study of structural and bulk defects in nanocrystalline samples of hydroxyapatite with a developed surface was carried out. The XRD method established distortions in the crystal lattice of the synthesized samples of hydroxyapatite (HAP), which are associated with the inclusion of impurity atoms present in the eggshell of birds used as a biological source of calcium. The presence of impurity atoms of magnesium, sodium, and fluorine in the obtained materials was determined by X-ray photoelectron spectroscopy. Applying ESR and Raman spectroscopy it was found the presence of CO3 complex in the structure. Studies of the morphological organization of the samples found a large number of surface defects – nanopores – in crystalline HAP. At the same time, the size of these 3D defects depends on the conditions of preparation and is determined by the content of phosphate groups in the initial solution.

Ultrafast growth of nanocrystalline graphene films by quenching and grain-size-dependent strength and bandgap opening

Nanocrystallization is a well-known strategy to dramatically tune the properties of materials; however, the grain-size effect of graphene at the nanometer scale remains unknown experimentally because of the lack of nanocrystalline samples. Here we report an ultrafast growth of graphene films within a few seconds by quenching a hot metal foil in liquid carbon source. Using Pt foil and ethanol as examples, four kinds of nanocrystalline graphene films with average grain size of ~3.6, 5.8, 8.0, and 10.3 nm are synthesized. It is found that the effect of grain boundary becomes more pronounced at the nanometer scale. In comparison with pristine graphene, the 3.6 nm-grained film retains high strength (101 GPa) and Young’s modulus (576 GPa), whereas the electrical conductivity is declined by over 100 times, showing semiconducting behavior with a bandgap of ~50 meV. This liquid-phase precursor quenching method opens possibilities for ultrafast synthesis of typical graphene materials and other two-dimensional nanocrystalline materials.

Temperature dependent dielectric properties and ac conductivity of GdFe1−xMnxO3 (0 ≤ x ≤ 0.3) perovskites

We have synthesized the nano-crystalline samples of GdFe1−xMnxO3(0 ≤ x ≤ 0.3) via solid state reaction route and studied their dielectric properties and ac conductivity in detail. X-ray diffraction patterns show monophase structure of the samples in orthorhombic crystal symmetry (space group Pbnm). The enhancement in dielectric constant is registered on Mn doping at room temperature as well as with the rise in temperature at a constant frequency. The fitting of Cole–Cole plots indicate the non-Debye kind relaxation mechanisms in the samples. The real (Z′) and imaginary (Z″) components of impedance reduce with the increase in frequency and Mn ions in GdFeO3 lattice. Nyquist plots are fitted to a single semicircle that hints towards the single relaxation process. The ac conductivity (σac) is also increased with the frequency and follow the power law,σac(ω) = Aωs wherein the exponent ‘s’ reduces with frequency. We have estimated the activation energies with the help of ln(σ) versus 1/T plots that remain almost constant below 350 K and show variation with the Mn doping in GdFeO3 perovskite at temperatures 620–673 K. The polaron hopping energy (WM) in the framework of the correlated barrier hopping (CBH) and non-overlapping small polaron tunneling (NSPT) models have been calculated and its variation with temperature signifies thermally activated conduction mechanism in the studied materials.

Effect of microstructure on crack behavior in nanocrystalline nickel using molecular dynamics simulation

The crack growth process in columnar nanocrystalline samples is simulated using the molecular dynamics method. The effects of grain size, grain boundary, crystallographic orientation and crack tip position on the crack growth behavior are investigated. Different sets of samples with mean grain sizes ranging from 4 nm to 14 nm are prepared. Samples with a similar number of grains and identical dimensions are considered for examining the impact of grain boundary and crystallographic orientation. To assess the effect of the grain boundary, no constraint is considered on the position and orientation of grains, while only the grain orientations are changed to examine the effect of crystallographic orientation. Also, samples with scaled dimensions are created to study the effect of grain size on the crack growth process. In such samples, the relative position of seeds and crystallographic orientation of grains remain constant. The results show that as the mean grain size is reduced, a higher level of stress is required for the initiation of crack growth. Moreover, the reduction of grain size from 14.24 nm to 11.65 nm increases the critical stress intensity factor. Further reduction of grain size decreases the critical stress intensity factor. For grain sizes smaller than 11.65 nm, the volume of stacking fault in the grains near the crack-tip is not significant. Grain size and grain boundary volume have a simultaneous impact on the initial slope which can be observed around the grain size of 11.65 nm. As a result, in nanocrystals with mean grain sizes of less than 11.65 nm, the crack grows in a brittle manner to reach the grain boundary, then progresses intergranularly with high speed. Consequently, grain boundaries and crystallographic orientations are not effective on the crack growth mechanism in nanocrystals with grain sizes less than 11.65 nm, whereas these factors can blunt or arrest the crack in nanocrystals with mean grain sizes of larger than 11.65 nm.

Microstructure investigation of r.f. current annealed FINEMET cold drawn microwires by UHR-TEM

The microstructure of FINEMET (Fe73.5Nb3Cu1Si13.5B9, at %) ferromagnetic microwires with diameters of 30 µm obtained by cold drawn of 120 µm thicker conventional amorphous microwires followed by radio frequency current annealing has been investigated by ultra-high resolution transmission electron (UHR-TEM) microscopy. The cold drawn microwires (CDWs) were annealed by radio frequency current of 375 mA@10MHz and 750 mA@10MHz, respectively, for 10 minutes to achieve cold drawn microwires with nano-crystalline structure. The specimens for UHR-TEM investigation were prepared in the shape of lamella using Focus Ion Beam microscope. For each annealed CDNWs were obtained two lamella one from the edge of microwire and another one from the center of the wire. Each specimen has been examined by transmission electron microscopy (TEM) using a Libra200MC microscope operated at 200kV through the bright-field and dark-field TEM, HR-TEM, HAADF STEM and EDX method. Electron diffraction patterns are interpreted using the computer programs SingleCrystal® and JEMS®. Mean grain size is measured using ImageJ software and making a geometrical correction for film thickness. The cold drawn microwires annealed at 350mA are largely amorphous, although containing occasional Fe3Si regions of short-range order as presented in Figure 1 (a). The cold drawn microwires annealed at 750mA present a nano-crystalline structures, with all nano-grains appearing to be of the bcc α-Fe(Si) structure as shown in Figure 1 (b). The estimated number density of nano-grains is 4.8 x 1023, which corresponds to an estimated phase fraction of 25 vol.% for a nano-grain radius of 5 nm. Line-scan EDX shows no particularly striking deviation from a homogenous distribution of elements for nanocrystalline sample, while a clustering behavior of elements for amorphous sample was observed.

Size-dependent magnetic properties of γ-Fe2O3 nanocrystallites

A route for synthesizing monodisperse magnetic nanocrystallites of maghemite, -Fe2O3, with various sizes has been revisited. A systematic investigation of three -Fe2O3 nanocrystalline samples by different techniques has been performed to characterize their size-dependent magnetic properties. Zero-field-cooled and field-cooled magnetization measurements reveal that the superparamagnetic blocking temperatures are around 230 K, 170 K, and 50 K for the 15.0 nm, 11.8 nm, and 6.1 nm nanocrystallites, respectively. Low-temperature Mössbauer spectra show that all three nanocrystallites have the maghemite structure with all the vacancies in the B-sites. Furthermore, detailed analysis shows that there are more vacancies on the B-sites for the 6.1 nm nanocrystallites compared to 0.33 for the bulk maghemite.

Impurity induced dielectric relaxor behavior in Zn doped LaFeO3

Sol–gel derived nanocrystalline samples of LaFe1−xZnxO3 have been investigated for their dielectric properties in the broad frequency and temperature range. The pristine sample exhibits an anomaly around Neel temperature in the variation of dielectric permittivity against temperature. However, the loss factor shows frequency dependent peak indicating the relaxational behavior in the LaFeO3 system. The incorporation of Zn enhances the relaxational behavior in the pristine system. A.C. conductivity is determined for all the samples in the temperature range 300–600 K. Activation energy determined in the high-temperature range (500–600 K) may correspond to the motion of singly ionized oxygen vacancies, in the vicinity of 450–500 K corresponds to the motion of doubly ionized oxygen vacancies within the single FeO6 octahedra and in the lower temperature range (300–450 K) it may correspond to hopping of electrons between Fe2+ and Fe3+ ions. The hopping conduction mechanism has been investigated from the temperature dependence of the “s” parameter. The conduction mechanism in pristine sample is governed by the correlated barrier hopping (CBH) model. However, in doped samples, the conduction mechanism follows both CBH and non-overlapping small polaron tunneling (NSPT) models.

Defects characterisation and studies of structural properties of sol–gel synthesised MgFe2O4 nanocrystals through positron annihilation and supportive spectroscopic methods

ABSTRACTMagnesium ferrite (MgFe2O4) nanocrystalline samples were prepared by sol–gel method and by sintering at temperatures from 300°C to 1000°C. X-ray diffraction and electron microscopic studies showed an increase in crystallite sizes and a decrease in lattice constants at higher sintering temperatures. UV-Vis absorption measurements depicted blue shift for samples of smaller crystallite sizes (dc) with a resultant increase of the band gap energies (Eg. = 2.07 eV at dc = 49 nm to 3.10 eV at dc = 6 nm, for samples sintered at 1000°C and 300°C, respectively). Fourier transform infrared spectroscopy of the samples proved the formation of the spinel structure while energy dispersive X-ray analysis pointed out the non-stoichiometric composition, which implied the presence of vacancy type defects that could modify the structural and magnetic characteristics of the compounds. This necessitated the use of positron annihilation lifetime and coincidence Doppler broadening spectroscopic studies for defect characterisation and the results indicated distinct redistribution of cations within the unit cells, making the compound overwhelmingly turn towards a normal spinel configuration at smaller nanocrystalline sizes. Positrons were trapped in larger vacancies of increasing numbers in smaller crystallites. The vacancies turned out to be formed at the octahedral sites where the increased ionic radius of Fe3+ became large enough to reduce the occupancy significantly. Mossbauer spectra analysis indicated an increase of the ferromagnetic properties in samples sintered at higher temperatures. At 300°C and 400°C, the samples dominantly showed paramagnetic behaviour.