Within this thesis, a comprehensive study of the initial growth process of pure Fe3O4 films and Fe3O4/NiO bilayers on Nb:SrTiO3(001) substrates including the thermal interdiffusion behavior of these bilayers is presented. The sensitive interplay between magnetic, electronic and structural properties of these materials has been investigated in detail. In the first study, the initial growth behavior of high-quality ultrathin magnetite films on SrTiO3(001) deposited by reactive molecular beam epitaxy depending on the deposition temperature has been analyzed. For this purpose, the growth process has been monitored in situ and during the deposition by grazing incidence x-ray diffraction (GIXRD). The second part provides a comparative study of Fe3O4/NiO bilayers grown on both MgO(001) and Nb:SrTiO3(001) substrates exploring morphological, structural and magnetic properties. These structures have been investigated by means of x-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), x-ray reflectivity (XRR) and diffraction (XRD), as well as vibrating sample magnetometry (VSM). Subsequently, thermal stability of these bilayers and the thermally induced interdiffusion process have been studied successively accompanied by a comprehensive characterization of the fundamental electronic, structural and magnetic properties using additional techniques such as angle resolved hard x-ray photoelectron spectroscopy (AR-HAXPES) and x-ray magnetic circular dichroism (XMCD). Finally, an alternative pathway for the preparation of ultrathin nickel ferrite films through interdiffusion is provided.

The aim of this thesis work was to develop magnetoelectric (ME) composites consisting of piezoelectric and magnetostrictive components. The piezoelectric constituent was selected as a PZT ceramic modified by strontium, bismuth and manganese. The magnetostrictive phase was nickel ferrite (NF) ceramic doped by cobalt, copper and manganese. The properties of component phases were optimized in order to enhance the ME effect in the composite. In the first part of the thesis, effects of sintering temperature on the dielectric and piezoelectric properties of PZT and on the electrical and magnetic properties of NF ceramics were investigated in the temperature range covered from 1150 to 1250 &deg / C. The best piezoelectric properties in PZT were attained at 1250 &deg / C. At this sintering temperature, values of piezoelectric strain coefficient, dielectric constant, and electromechanical coupling coefficient were 434 pC/N, 1320 and 0.48, respectively. NF ceramics showed poor densification / 80 %TD was attained at 1250 &deg / C. In order to obtain higher densities in ferrites, Bi2O3 was used as a sintering aid. Addition of Bi2O3 enhanced densification up to 97 %TD, and improved electrical and magnetic properties of ferrites. Highest DC-resistivity of 1.15*10^8 ohm-cm and highest magnetostriction of ~26 ppm were attained in NF ceramics doped with 1 wt% Bi2O3. In the second part of the thesis, ME composites were manufactured either as bulk composites or as laminated composites. The efficiency of different composite types was evaluated in terms of voltage output in response to the applied magnetic field. Higher outputs were observed in laminated composites.

Neste estudo apresenta-se a síntese de duas amostras de nanopartículas de ferrita de níquel, denominadas C-NiFe2O4 e NiFe2O4, através de um método simples, de baixo custo e ambientalmente amigável. Estudos morfológicos, estruturais, eletrônicos, ópticos e magnéticos foram realizados com o intuito de caracterizar as propriedades desses materiais para que possibilitassem, além de maior grau de conhecimento, sua aplicação como sensores colorimétricos para detecção de ácido ascórbico e peróxido de hidrogênio. Mediante a análise térmica dos precursores, foi possível determinar os intervalos de temperatura de decomposição, assim como a temperatura ótima de formação das nanopartículas. A amostra NiFe2O4 é ferromagnética e corresponde a uma fase cúbica de espinélio inverso. Os dados de difração de raios X, espectroscopia Mössbauer e o modelo iônico sugerem a presença de um certo grau de substituição, possuindo em sua estrutura um cátion divalente como agente dopante. As nanopartículas de C-NiFe2O4 foram utilizadas como catalisador na oxidação do 3,3',5,5'-tetrametilbenzidina (TMB) em meio ácido para formar uma solução azul sem adição de outro reagente. Como resultado foi utilizado como sensor colorimétrico para detecção de ácido ascórbico, visto que este reduz o complexo de transferência de carga, TMBOX, novamente para TMB. A calibração analítica apresentou uma faixa linear entre 1-20 μM para a concentração de ácido ascórbico, com limite de detecção (3/m) de 0,93 μM. A determinação em suplementos de vitamina C através do método de adição de padrão mostrou a eficiência do sensor para detectar ácido ascórbico em amostras reais. Já a amostra de NiFe2O4 demonstrou atividade catalítica semelhante as peroxidases naturais, oxidando o TMB na presença de H2O2 para formar TMBOX, que dá coloração azul a solução. Dessa forma, NiFe2O4 foi utilizado em um sensor colorimétrico para detecção de H2O2 e a calibração analítica revelou duas faixas lineares, uma entre 2,28 - 28,60 μM e a outra entre 28,60 μM - 114,20 μM. O limite de detecção (3/m) foi de 1,94 μM. Ambos os métodos apresentaram boa repetibilidade, com coeficiente de variação de 3,5% e 4% respectivamente. / This study presents the synthesis of two samples of nickel ferrite nanoparticles, termed C-NiFe2O4 and NiFe2O4, through a simple, low cost and environmentally friendly method. Morphological, structural, electronic, optical and magnetic studies were carried out with the aim of characterizing the properties of these materials, which allowed the application of colorimetric sensors for the detection of ascorbic acid and hydrogen peroxide. Through the thermal analysis of the precursors, it was possible to determine the decomposition temperature ranges, as well as the optimum temperature of formation of the nanoparticles. The sample NiFe2O4 is ferromagnetic and corresponds to a cubic phase of inverse spinel. The X-ray diffraction data, Mössbauer spectroscopy and the ionic model suggest the presence of a certain degree of substitution, having in its structure a divalent cation as a doping agent. The C-NiFe2O4 nanoparticles were used as catalysts in the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in acidic medium to form a blue solution without addition of another reagent. As a result, it was used as a colorimetric sensor for the detection of ascorbic acid, as it reduces the charge transfer complex, TMBOX, again to TMB. The analytical calibration showed a linear range between 1-20 μM for the concentration of ascorbic acid, with a detection limit (3 /m) of 0.93 μM. The determination of vitamin C supplements using the standard addition method showed the efficiency of the sensor to detect ascorbic acid in actual samples. Already NiFe2O4 sample demonstrated catalytic activity similar to natural peroxidases, oxidizing the TMB in the presence of H2O2 to form TMBOX, which gives blue coloration to the solution. Thus, NiFe2O4 was used in a colorimetric sensor to detect H2O2, and the analytical calibration revealed two linear ranges, one between 2.28 - 28.60 μM and the other between 28.60 μM - 114.20 μM. The detection limit (3 /m) was 1.94 μM. Both methods presented good repeatability, with a coefficient of variation of 3.5% and 4% respectively.

Neste estudo apresenta-se a síntese de duas amostras de nanopartículas de ferrita de níquel, denominadas C-NiFe2O4 e NiFe2O4, através de um método simples, de baixo custo e ambientalmente amigável. Estudos morfológicos, estruturais, eletrônicos, ópticos e magnéticos foram realizados com o intuito de caracterizar as propriedades desses materiais para que possibilitassem, além de maior grau de conhecimento, sua aplicação como sensores colorimétricos para detecção de ácido ascórbico e peróxido de hidrogênio. Mediante a análise térmica dos precursores, foi possível determinar os intervalos de temperatura de decomposição, assim como a temperatura ótima de formação das nanopartículas. A amostra NiFe2O4 é ferromagnética e corresponde a uma fase cúbica de espinélio inverso. Os dados de difração de raios X, espectroscopia Mössbauer e o modelo iônico sugerem a presença de um certo grau de substituição, possuindo em sua estrutura um cátion divalente como agente dopante. As nanopartículas de C-NiFe2O4 foram utilizadas como catalisador na oxidação do 3,3',5,5'-tetrametilbenzidina (TMB) em meio ácido para formar uma solução azul sem adição de outro reagente. Como resultado foi utilizado como sensor colorimétrico para detecção de ácido ascórbico, visto que este reduz o complexo de transferência de carga, TMBOX, novamente para TMB. A calibração analítica apresentou uma faixa linear entre 1-20 μM para a concentração de ácido ascórbico, com limite de detecção (3/m) de 0,93 μM. A determinação em suplementos de vitamina C através do método de adição de padrão mostrou a eficiência do sensor para detectar ácido ascórbico em amostras reais. Já a amostra de NiFe2O4 demonstrou atividade catalítica semelhante as peroxidases naturais, oxidando o TMB na presença de H2O2 para formar TMBOX, que dá coloração azul a solução. Dessa forma, NiFe2O4 foi utilizado em um sensor colorimétrico para detecção de H2O2 e a calibração analítica revelou duas faixas lineares, uma entre 2,28 - 28,60 μM e a outra entre 28,60 μM - 114,20 μM. O limite de detecção (3/m) foi de 1,94 μM. Ambos os métodos apresentaram boa repetibilidade, com coeficiente de variação de 3,5% e 4% respectivamente. / This study presents the synthesis of two samples of nickel ferrite nanoparticles, termed C-NiFe2O4 and NiFe2O4, through a simple, low cost and environmentally friendly method. Morphological, structural, electronic, optical and magnetic studies were carried out with the aim of characterizing the properties of these materials, which allowed the application of colorimetric sensors for the detection of ascorbic acid and hydrogen peroxide. Through the thermal analysis of the precursors, it was possible to determine the decomposition temperature ranges, as well as the optimum temperature of formation of the nanoparticles. The sample NiFe2O4 is ferromagnetic and corresponds to a cubic phase of inverse spinel. The X-ray diffraction data, Mössbauer spectroscopy and the ionic model suggest the presence of a certain degree of substitution, having in its structure a divalent cation as a doping agent. The C-NiFe2O4 nanoparticles were used as catalysts in the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in acidic medium to form a blue solution without addition of another reagent. As a result, it was used as a colorimetric sensor for the detection of ascorbic acid, as it reduces the charge transfer complex, TMBOX, again to TMB. The analytical calibration showed a linear range between 1-20 μM for the concentration of ascorbic acid, with a detection limit (3 /m) of 0.93 μM. The determination of vitamin C supplements using the standard addition method showed the efficiency of the sensor to detect ascorbic acid in actual samples. Already NiFe2O4 sample demonstrated catalytic activity similar to natural peroxidases, oxidizing the TMB in the presence of H2O2 to form TMBOX, which gives blue coloration to the solution. Thus, NiFe2O4 was used in a colorimetric sensor to detect H2O2, and the analytical calibration revealed two linear ranges, one between 2.28 - 28.60 μM and the other between 28.60 μM - 114.20 μM. The detection limit (3 /m) was 1.94 μM. Both methods presented good repeatability, with a coefficient of variation of 3.5% and 4% respectively.

Neste estudo apresenta-se a síntese de duas amostras de nanopartículas de ferrita de níquel, denominadas C-NiFe2O4 e NiFe2O4, através de um método simples, de baixo custo e ambientalmente amigável. Estudos morfológicos, estruturais, eletrônicos, ópticos e magnéticos foram realizados com o intuito de caracterizar as propriedades desses materiais para que possibilitassem, além de maior grau de conhecimento, sua aplicação como sensores colorimétricos para detecção de ácido ascórbico e peróxido de hidrogênio. Mediante a análise térmica dos precursores, foi possível determinar os intervalos de temperatura de decomposição, assim como a temperatura ótima de formação das nanopartículas. A amostra NiFe2O4 é ferromagnética e corresponde a uma fase cúbica de espinélio inverso. Os dados de difração de raios X, espectroscopia Mössbauer e o modelo iônico sugerem a presença de um certo grau de substituição, possuindo em sua estrutura um cátion divalente como agente dopante. As nanopartículas de C-NiFe2O4 foram utilizadas como catalisador na oxidação do 3,3',5,5'-tetrametilbenzidina (TMB) em meio ácido para formar uma solução azul sem adição de outro reagente. Como resultado foi utilizado como sensor colorimétrico para detecção de ácido ascórbico, visto que este reduz o complexo de transferência de carga, TMBOX, novamente para TMB. A calibração analítica apresentou uma faixa linear entre 1-20 μM para a concentração de ácido ascórbico, com limite de detecção (3/m) de 0,93 μM. A determinação em suplementos de vitamina C através do método de adição de padrão mostrou a eficiência do sensor para detectar ácido ascórbico em amostras reais. Já a amostra de NiFe2O4 demonstrou atividade catalítica semelhante as peroxidases naturais, oxidando o TMB na presença de H2O2 para formar TMBOX, que dá coloração azul a solução. Dessa forma, NiFe2O4 foi utilizado em um sensor colorimétrico para detecção de H2O2 e a calibração analítica revelou duas faixas lineares, uma entre 2,28 - 28,60 μM e a outra entre 28,60 μM - 114,20 μM. O limite de detecção (3/m) foi de 1,94 μM. Ambos os métodos apresentaram boa repetibilidade, com coeficiente de variação de 3,5% e 4% respectivamente. / This study presents the synthesis of two samples of nickel ferrite nanoparticles, termed C-NiFe2O4 and NiFe2O4, through a simple, low cost and environmentally friendly method. Morphological, structural, electronic, optical and magnetic studies were carried out with the aim of characterizing the properties of these materials, which allowed the application of colorimetric sensors for the detection of ascorbic acid and hydrogen peroxide. Through the thermal analysis of the precursors, it was possible to determine the decomposition temperature ranges, as well as the optimum temperature of formation of the nanoparticles. The sample NiFe2O4 is ferromagnetic and corresponds to a cubic phase of inverse spinel. The X-ray diffraction data, Mössbauer spectroscopy and the ionic model suggest the presence of a certain degree of substitution, having in its structure a divalent cation as a doping agent. The C-NiFe2O4 nanoparticles were used as catalysts in the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in acidic medium to form a blue solution without addition of another reagent. As a result, it was used as a colorimetric sensor for the detection of ascorbic acid, as it reduces the charge transfer complex, TMBOX, again to TMB. The analytical calibration showed a linear range between 1-20 μM for the concentration of ascorbic acid, with a detection limit (3 /m) of 0.93 μM. The determination of vitamin C supplements using the standard addition method showed the efficiency of the sensor to detect ascorbic acid in actual samples. Already NiFe2O4 sample demonstrated catalytic activity similar to natural peroxidases, oxidizing the TMB in the presence of H2O2 to form TMBOX, which gives blue coloration to the solution. Thus, NiFe2O4 was used in a colorimetric sensor to detect H2O2, and the analytical calibration revealed two linear ranges, one between 2.28 - 28.60 μM and the other between 28.60 μM - 114.20 μM. The detection limit (3 /m) was 1.94 μM. Both methods presented good repeatability, with a coefficient of variation of 3.5% and 4% respectively.

Within this thesis, (ultra)thin NiFe2O4 (NFO) and CoFe2O4 (CFO) films are prepared via reactive molecular beam epitaxy (RMBE) on MgO(001) and SrTiO3(001) substrates and are characterized in terms of their structural, electronic, and magnetic properties. In a first step, the structural properties of ultrathin off-stoichiometric NixFe(3-x)O4 films (0<x<1.5) deposited via RMBE on MgO(001) are investigated in situ during film deposition by means of synchrotron radiation-based x-ray diffraction (XRD) and ex situ after film growth by high energy surface x-ray diffraction (HESXRD). In the second major step of this work, a more extensive study on the dependence of the cationic ratio in NixFe(3-x)O4 thin films (0<x<2.07) grown on MgO(001) is conducted. The film surface structure and chemical composition is characterized in situ by low energy electron diffraction (LEED) and laboratory-based soft x-ray photoelectron spectroscopy (XPS), respectively. Film thicknesses are determined via analysis of x-ray reflectivity (XRR) data, while the film structure is analyzed by XRD measurements. Further, chemical properties and the electronic structure of the NFO films with focus on the cationic valencies of Ni and Fe cations with varying x is investigated by means of (angle-resolved) hard x-ray photoelectron spectroscopy [(AR-)HAXPES]. Complementary x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) investigations are conducted to obtain information on the cationic site occupancies and on the element-specific magnetic moments. The latter are compared to magnetic properties characterized via superconducting quantum interference device (SQUID) magnetometry. In a third step, the type of substrate is changed to SrTiO3(001) to investigate the influence of a larger strain applied by the substrate to NFO films with varying thicknesses. Structural characterization at the surfaces and in the films is conducted by means of LEED, XRR, and (grazing incidence) XRD, whereas XPS and HAXPES provide information on the chemical composition and electronic structure in the near-surface region and in deeper subsurface layers, respectively. Magnetic properties are characterized by SQUID magnetometry. In a fourth step, an alternative pathway for the formation of ferrite thin films is demonstrated exemplarily for CoFe2O4 films on SrTiO3(001), which are formed by interdiffusion of Fe3O4/CoO bilayers. The interdiffusion process was monitored via XRR, soft XPS and AR-HAXPES to determine the bilayer/film structure, stoichiometry, and chemical properties. Analysis of complementary XAS measurements provides additional information on the occupancies of Fe and Co cations during interdiffusion. Final SQUID magnetometry measurements are performed to gain information on the magnetic properties before and after complete interdiffusion. Overall, within this thesis, it was demonstrated that NFO and CFO thin films can be prepared in high structural quality with sharp interfaces and surfaces, which is crucial for the applicability in the fields of spintronics and spincaloritronics.

Selective oxidation and sulfation roasting of nickel concentrate followed by leaching was investigated as a novel route for nickel production. In the oxidation roasting stage, the iron species in the nickel concentrate was preferentially oxidized to form iron oxides, leaving non-ferrous metals (Ni, Cu, Co) as sulfides. The roasted product was then sulfation roasted to convert the sulfides of the latter metals into water-soluble sulfates. The sulfates were then leached into solution for further recovery and separation from iron oxides. The oxidation of nickel concentrate was firstly studied by means of thermogravimetric and differential thermal analysis over a wide temperature range. A reaction scheme was deduced, in which preferential oxidation of iron sulfide species occurred over a wide temperature range up to about 700 ºC, forming a Ni1-xS core with iron oxide shell. A batch fluidized bed roaster was then constructed to study the oxidation and sulfation roasting of nickel sulfide concentrate. Oxidation roasting tests were carried out at temperatures between 650 °C and 775 °C. It was found that low temperatures (e.g. 650 °C) are favorable for the preferential oxidation of iron sulfide species while minimizing the formation of nickeliferous oxides, i.e. trevorite and NiO. Several parameters were varied in the sulfation roasting experiments, including the sulfation gas flowrate, sulfation roasting temperature, the addition of Na2SO4, sulfation roasting time, and the oxidation roasting temperature. Under optimized conditions of sulfation gas composition (95% air, 5% SO2), temperature (700 °C), Na2SO4 addition (10 wt%) and time (150 min), the conversions to sulfates were 79% Ni, 91% Cu, and 91% Co. Only 5% Fe forms water-soluble sulfate. The residue from the leaching of calcine in water contained 49% Fe and 10% Ni, which is a suitable feedstock for the production of ferronickel alloys. Therefore, further studies were also conducted to evaluate the reduction behavior of the residue with CO, H2 and graphite.

Des nanoparticules de ferrite de nickel ont été produites par une technique de plasma induc-tif à jet de solution. En contrôlant le ratio Ni/(Ni+Fe) dans la solution de précurseurs, une grande gamme de nanoparticules monophasées de ferrite de nickel NixFe3-xO4-δ (0 ≤ x ≤ 1) peuvent être produites, ainsi que des nanoparticules multiphasées de NiFe2O4 + (Ni,Fe)O. Des nanoparticules avec deux types de morphologie peuvent être obtenues dépendant de l’endroit où elles sont recueillies dans le réacteur : des octaèdres tronqués facettés, ayant une taille moyenne de 30 nm, ou un petit agglomérat de forme aléatoire, ayant une taille caractéristique de ~3-5 nm. Pour les nanoparticules multiphasées, il est démontré que la phase (Ni,Fe)O se dépose de façon sélective sur les facettes {110} et {111} de la ferrite de nickel, tout en laissant les facettes {100} exposées. En utilisant la même procédure, il est également possible de produire des nanocubes de NiO. Ces résultats démontrent la flexibilité des réacteurs à plasma inductif pour la production de nanoparticules mono ou multiphasées organisées avec un grand rendement. Des analyses de DRX in situ sur ces nanoparticules montrent que la réduction avec H2 enlève l'excès d'oxygène de la maille spinelle, si présent initialement, suivi d'une réduction vers les alliages métalliques (Ni,Fe). Leur réoxydation subséquente avec CO2 mène à un renversement partiel du processus de réduction par H2. Les expériences in situ ont été analysées avec un modèle cristallin qui lie le paramètre de maille d'un spinelle à sa déviation de sa stœchiométrie en oxygène (δ). / Abstract : Nickel ferrite spinel nanoparticles were produced by the solution spray induction plasma technique. By controlling the Ni/(Ni+Fe) ratio in the precursor solution, a wide range of single-phased nickel ferrite NixFe3-xO4-δ (0 ≤ x ≤ 1) nanoparticles can be produced, along with multiphased NiFe2O4 + (Ni,Fe)O nanoparticles. Nanoparticles with two types of morphologies can be obtained depending on where they are collected in the reactor: facetted truncated octa-hedrons, with an average size of about 30 nm, or a small-sized random agglomerate, with a characteristic length of ~3-5 nm. For the multiphased nanoparticles, it is demonstrated that the (Ni,Fe)O phase selectively deposits on the {110} and {111} facets of nickel ferrite, while leaving its {100} facet exposed. Using the same procedure, it is also possible to produce nanocubes of NiO. These results show the flexibility of the induction plasma method for the production of organized single or multiphased nanoparticles with a high throughput. In situ XRD catalytic experiments on those nanoparticles show that reduction with H2 will cause the removal of excess oxygen from the spinel lattice, if present initially, followed by a reduction to metallic (Ni,Fe) alloys. Their subsequent reoxidation with CO2 leads to a partial reversal of the H2 reduction process. In situ experiments were enhanced by the development of a crystal-lographic model that links the lattice parameter of a spinel to its deviation from oxygen stoechiometry (δ).

Axial offset anomaly (AOA) in pressurized water reactors (PWR) refers to deviation of the measured neutron flux in the top half of the core from the predicted values. Among other difficulties, AOA reduces the shutdown margin, and may force the plant to reduce power output. AOA is believed to be caused by three related phenomena occurring in the core while operating at full power: sub-cooled nucleate boiling concentrated mainly in the upper half of the core, corrosion product deposition on the cladding surface (crud), and the deposition of boron within the porous crud layer in regions of vigorous sub-cooled boiling. This study replicates the conditions within the PWR primary coolant; specifically, the temperature, pressure, peak surface heat flux, coolant velocity and water chemistry are simulated in order to produce prototypical crud on an electrically heated Zircaloy-4 test element. At the conclusion of each test run, the heated Zircaloy-4 test element is rapidly isolated from the coolant in order to trap any soluble boron species that may be present in the crud layer. The results of this investigation indicate that prototypical crud with significant boron deposition can be produced. The deposited boron compound has been determined to be lithium tetraborate (Li2B4O7). Comparative experiments have been run to determine the effect of coolant pH, concentration and type of additives, and duration of exposure on the thickness of the crud deposit. The data obtained in this investigation can be used to validate mechanistic models for crud deposition and AOA in pressurized water reactors.

This thesis describes the convenient routes and the preparation conditions (temperature, oxygen partial presssure) which lead to the formation of single phase materials within the quaternary system Cu-Ni-Fe-O. The investigated compositions are the solid solutions CuxNi1-xFe2O4, the ferrites occurring in the phase triangle Cu0.5Ni0.5Fe2O4 -Cu0.9Fe2.1O4 - Cu0.5Fe2.5O4 and some copper-nickel oxide solid solutions. Three synthesis routes have been used, namely (i) the preparation and the thermal decomposition of freeze-dried carboxylate precursors, (ii) the preparation and the oxidation of intermetallic phases and (iii) the preparation and the heat treatment in air of mixed oxide/metallic powders. The thermal decomposition of freeze-dried Cu-Ni-Fe formate has been found as a suitable method for preparing single spinel phases within the Cu-Ni-Fe-O system. In comparison with the conventional solid state reaction, the required temperature is much lower. Concerning the solid solution CuxNi1-xFe2O4 , a single phase spinel is formed at 1000¢XC for x &amp;lt; 0.7; for CuO is identified as second phase. In this latter range the formation of a pure phase required an increase of the iron content in the mixture. The other single spinel phases in the phase triangle Cu0.5Ni0.5Fe2O4 - Cu0.9Fe2.1O4 - Cu0.5Fe2.5O4 have been synthesized under special synthesis p(O2)/T-conditions. For copper ferrites Cu1-xFe2+xO4 with x ?­ 0.1, 0.2, 0.33, 0.4 and 0.5, the change in the conductivity with the temperature is irreversible. The deviation from the linearity of the conductivity ?ã as a function of the temperature occurs due to the thermal history of these samples. The saturation magnetic moment (nB) at 5K, of some synthesized CuxNi1-xFe2O4 compounds has been determined. It has been found that nB increases with the nickel content in the ferrite sample.