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Single-phase chalcopyrite (CuFeS2) is a key reference material in the development of new metallurgicalprocesses to ensure a reliable copper supply. Here, we report on the successful synthesis of single-phase chalcopyrite and its phase behaviour. Single-phase chalcopyrite (CuFeS2) is a key reference material in the development of new metallurgical processes to ensure a reliable copper supply. Here, we report on the successful synthesis of single-phase chalcopyrite and its phase behaviour. We further rationalise different opinions previously expressed in the literature. Chalcopyrite synthesis has been studied at 450 °C with varying sulfur contents and analysed using X-ray powder diffraction (XRPD) and 57Fe-Mössbauer spectroscopy. With stoichiometric amounts (Cu[thin space (1/6-em)]:[thin space (1/6-em)]Fe[thin space (1/6-em)]:[thin space (1/6-em)]S = 25[thin space (1/6-em)]:[thin space (1/6-em)]25[thin space (1/6-em)]:[thin space (1/6-em)]50) the main chalcopyrite phase is contaminated with pyrite (FeS2) and bornite (Cu5FeS4). Single-phase chalcopyrite was only found in samples containing around 49.7 at% sulfur in the reactant mixture. Mößbauer spectroscopy confirmed that chalcopyrite contains trivalent iron. Temperature dependent XRPD measurements detected an order–disorder phase transition starting at 485 °C. At temperatures above 535 °C, samples only contained intermediate solid solutions. These adopt the sphalerite structure with the lattice constant slightly varying with Cu[thin space (1/6-em)]:[thin space (1/6-em)]Fe ratio.

In this thesis the superconducting and magnetic phases of LiOH(Fe,Co)(Se,S), CuFeAs/CuFeSb, and LaFeP_1-xAs_xO - belonging to the 11, 111 and 1111 structural classes of iron-based arsenides and chalcogenides - are investigated by means of 57Fe Mössbauer spectroscopy and muon spin rotation/relaxation (μSR). Of major importance in this study is the application of high magnetic fields in Mössbauer spectroscopy to distinguish and characterize ferro- (FM) and antiferromagnetic (AFM) order. A user-friendly Mössbauer data analysis program was developed to provide suitable model functions not only for high field spectra, but relaxation spectra or parameter distributions in general. In LaFeP_1-xAs_xO the reconstruction of the Fermi surface is described by the vanishing of the Γ hole pocket with decreasing x. The continuous change of the orbital character and the covalency of the d-electrons is shown by Mössbauer spectroscopy. A novel antiferromagnetic phase with small magnetic moments of ~ 0.1 μ_B state is characterized. The superconducting order parameter is proven to continuously change from a nodal to a fully gapped s-wave like Fermi surface in the superconducting regime as a function of x, partially investigated on (O,F) substituted samples. LiOHFeSe is one of the novel intercalated FeSe compounds, showing strongly increased T_C = 43 K mainly due to increased interlayer spacing and resulting two-dimensionality of the Fermi surface. The primary interest of the samples of this thesis is the simultaneously observed ferromagnetism and superconductivity. The local probe techniques prove that superconducting sample volume gets replaced by ferromagnetic volume. Ferromagnetism arises from magnetic order with T_C = 10 K of secondary iron in the interlayer. The tendency of this system to show (Li,Fe) disorder is preserved upon (Se,S) substitution. However, superconductivity gets suppressed. The results of Mössbauer spectroscopy indicate that the systems tends to a secondary structural phase, where the local iron environment observed in pure FeS is absent. Moreover, two interlayer positions of the iron are identified. The absence of enhanced superconducting T_C in LiOHFeS thus is related to a structural instability. Also, in CuFeAs the role of secondary iron at the Cu position turns out to be decisive for the observed magnetic behaviour. As in LiOHFeSe, it orders ferromagnetically at T_C ~ 11 K and superimposes with the magnetic instability of the main iron site. It is shown that a small charge doping of 0.1e/Fe, which is expected from (Cu,Fe) disorder, is sufficient to switch the system between a paramagnetic and an AFM ground state. Both magnetic orders are indistinguishable, because the magnetic order parameters are strongly coupled. This coupling was observed in the structurally identical CuFeSb, where the magnetic order parameters of both iron sites scale perfectly. The magnetically unstable CuFeAs and the ferromagnetic CuFeSb can be classified according to the theory of As height driven magnetism, predicting a change from paramagnetism to AFM and finally FM with increasing As height.

In this thesis the superconducting and magnetic phases of LiOH(Fe,Co)(Se,S), CuFeAs/CuFeSb, and LaFeP_1-xAs_xO - belonging to the 11, 111 and 1111 structural classes of iron-based arsenides and chalcogenides - are investigated by means of 57Fe Mössbauer spectroscopy and muon spin rotation/relaxation (μSR). Of major importance in this study is the application of high magnetic fields in Mössbauer spectroscopy to distinguish and characterize ferro- (FM) and antiferromagnetic (AFM) order. A user-friendly Mössbauer data analysis program was developed to provide suitable model functions not only for high field spectra, but relaxation spectra or parameter distributions in general. In LaFeP_1-xAs_xO the reconstruction of the Fermi surface is described by the vanishing of the Γ hole pocket with decreasing x. The continuous change of the orbital character and the covalency of the d-electrons is shown by Mössbauer spectroscopy. A novel antiferromagnetic phase with small magnetic moments of ~ 0.1 μ_B state is characterized. The superconducting order parameter is proven to continuously change from a nodal to a fully gapped s-wave like Fermi surface in the superconducting regime as a function of x, partially investigated on (O,F) substituted samples. LiOHFeSe is one of the novel intercalated FeSe compounds, showing strongly increased T_C = 43 K mainly due to increased interlayer spacing and resulting two-dimensionality of the Fermi surface. The primary interest of the samples of this thesis is the simultaneously observed ferromagnetism and superconductivity. The local probe techniques prove that superconducting sample volume gets replaced by ferromagnetic volume. Ferromagnetism arises from magnetic order with T_C = 10 K of secondary iron in the interlayer. The tendency of this system to show (Li,Fe) disorder is preserved upon (Se,S) substitution. However, superconductivity gets suppressed. The results of Mössbauer spectroscopy indicate that the systems tends to a secondary structural phase, where the local iron environment observed in pure FeS is absent. Moreover, two interlayer positions of the iron are identified. The absence of enhanced superconducting T_C in LiOHFeS thus is related to a structural instability. Also, in CuFeAs the role of secondary iron at the Cu position turns out to be decisive for the observed magnetic behaviour. As in LiOHFeSe, it orders ferromagnetically at T_C ~ 11 K and superimposes with the magnetic instability of the main iron site. It is shown that a small charge doping of 0.1e/Fe, which is expected from (Cu,Fe) disorder, is sufficient to switch the system between a paramagnetic and an AFM ground state. Both magnetic orders are indistinguishable, because the magnetic order parameters are strongly coupled. This coupling was observed in the structurally identical CuFeSb, where the magnetic order parameters of both iron sites scale perfectly. The magnetically unstable CuFeAs and the ferromagnetic CuFeSb can be classified according to the theory of As height driven magnetism, predicting a change from paramagnetism to AFM and finally FM with increasing As height.:1 Acronyms and Symbols 2 Introduction 3 Iron-based arsenides and chalcogenides 3.1 Structural properties 3.2 Electronic properties 3.2.1 Magnetism 3.2.2 Superconductivity 3.2.3 Nematic phase 3.3 Investigated samples 4 Moessfit - a free Mössbauer fitting program 4.1 Aspects of program design 4.2 Errors 4.2.1 Uncorrelated 4.2.2 Hesse 4.2.3 MonteCarlo 4.2.4 Minos 4.3 Fitting algorithm 4.4 Maximum entropy method (MEM) 4.5 Kolmogorov-Smirnov confidence 5 Mössbauer spectroscopy 5.1 Mössbauer effect 5.2 Relativistic Doppler effect 5.3 Full static Hamiltonian 5.3.1 Quadrupole interaction 5.3.2 Isomer shift. 5.3.3 Zeeman splitting 5.3.4 Combined interaction 5.3.5 Transition probabilities 5.3.6 The magic angle 5.4 Transmission integral 5.4.1 Absorption area 5.4.2 Ideal thickness 5.4.3 Line width and line shape 5.4.4 Levelling 5.5 Applied field measurements of powder samples 5.5.1 Paramagnet, axial symmetric EFG in transverse field geometry 6 5.5.2 Uniaxial antiferromagnet, axial symmetric EFG in transverse field geometry 6 5.5.3 Paramagnet, axial symmetric EFG in longitudinal field geometry 6 5.5.4 Uniaxial ferromagnet, axial symmetric EFG in transverse field geometry 6 5.5.5 Polarised photons 5.5.6 Total absorption cross section 5.5.7 Polarised sources 5.6 Blume line shape model 6 μSR 6.1 Muon decay and detection 6.2 Magnetic order and dynamic relaxation 6.2.1 Magnetic order 6.2.2 Time dependent field distributions 6.2.3 Aspects of μSR in iron-based arsenides and chalcogenides 6.2.4 Weak transverse field (WTF) 6.3 Superconductivity - transverse field (TF) experiments 7 Intercalated FeSe 7.1 Bulk properties: XRD, susceptibility, resistivity 7.2 Structural characterization 7.3 LiOHFeSe - Mössbauer spectroscopy 7.3.1 Applied transverse field 7.4 LiOHFeSe - μSR 7.4.1 Zero field (ZF) 7.4.2 Pinning experiment 7.4.3 Transverse field (TF) 7.5 Mössbauer investigation of LiOHFe_1-yCo_ySe_1-xS_x. 7.6 Discussion 8 LaFeO(As,P) 8.1 Preliminary measurements and electronic structure calculations 8.2 Mössbauer spectroscopy 8.3 μSR 8.3.1 Magnetic characterization 8.3.2 Spin dynamics 8.3.3 Superconductivity 8.4 Discussion 9 CuFeAs and CuFeSb 9.1 Preliminary results of CuFeAs and CuFeSb 9.2 CuFeAs: Mössbauer spectroscopy 9.2.1 Zero field (ZF) 9.2.2 Longitudinal field (LF) 9.2.3 Transverse field (TF) 9.3 CuFeAs: μSR 9.3.1 Zero field (ZF) 9.3.2 Weak transverse field (WTF) 9.4 Further investigations on CuFeAs 9.4.1 Neutron scattering 9.4.2 Theoretical calculation 9.4.3 Local element analysis with EDX/WDX 9.5 CuFeSb: Mössbauer spectroscopy 9.5.1 Zero Field (ZF) 9.5.2 Transverse field (TF) 9.6 Discussion 10 Conclusion 11 Appendix 11.1 Derivation of the quadrupole interaction and isomer shift 11.2 Matrix form of the static nuclear Hamiltonian 11.3 Mössbauer line intensities 11.4 Blume line shape model 11.4.1 Special case: two states with diagonal Hamiltonians 11.5 Moessfit models 11.5.1 FeSe_1-xS_x(Li_1-zFe_zOH) ZF, standard 11.5.2 FeSe_1-xS_x(Li_1-zFe_zOH) ZF, 4 fractions 11.5.3 FeSe_1-xS_x(Li_1-zFe_zOH) Pinning 11.5.4 FeSe_1-xS_x(Li_1-zFe_zOH) TF 11.5.5 FeSe_1-xS_x(Li_1-zFe_zOH) CS-Vzz-MEM 11.5.6 LaFeP_1-xAs_x+ ferrocene, ZF 11.5.7 LaFeP_1-xAs_x+ ferrocene, LF 11.5.8 LaFeP_1-xAs_x+ iron foil, ZF 11.5.9 LaFeAsO ZF 11.5.10 LaFeAsO TF 11.5.11 CuFeAs + ferrocen, ZF 11.5.12 CuFeAs + ferrocen, ZF, high statistics 11.5.13 CuFeAs + ferrocen, LF 11.5.14 CuFeAs + ferrocen, TF 11.5.15 CuFeSb ZF 11.5.16 CuFeSb TF

Neste trabalho, estudou-se a síntese por sol-gel da ferrita de cobalto (CoFe2O4), variando-se a temperatura de tratamento térmico do xerogel. Nitrato de ferro e nitrato de cobalto foram utilizados como fonte de cátions e ácido cítrico como mineralizador. Os produtos obtidos, tratados a 750, 800 e 850°C, tiveram sua microestrutura e propriedades magnéticas investigadas no intuito de encontrar correlações entre as condições de síntese, as posições ocupadas pelos cátions dentro da estrutura espinélio do composto e as propriedades magnéticas medidas. Estudos de difratometria de raios X exibiram reflexões características da estrutura espinélio, o que sugere que o tratamento térmico não afetou significativamente a estrutura cristalina do material. Uma fração secundária de hematita também foi observada. As ferritas apresentaram área superficial específica (por BET) de aproximadamente 4 m².g-1. Imagens por MEV indicam que o material apresenta-se aglomerado. Quanto às propriedades magnéticas, um máximo de coercividade de 1405.2 Oersted foi encontrado para a amostra tratada a 800°C. Espectros Mößbauer indicaram um baixo grau de inversão nos espinélios formados, o que é incomum para a ferrita de cobalto. Subtraindo do espectro obtido por Mößbauer o excesso de ferro na forma de hematita, há um forte indicativo que a ferrita foi sintetizada de maneira sub-estequiométrica deficiente em ferro. / We herein report a study on the sol-gel synthesis of cobalt ferrite (CoFe2O4) and the effect of treatment temperature on the product outcome. Iron nitrate and cobalt nitrate were used as cation sources and citric acid as mineralizer. Products treated at 750, 800 and 850°C had their microstructure and magnetic properties assessed in order to correlate their synthesis conditions, the positions in which the cations are inserted in the spinel structure and the magnetic behavior displayed by the ferrites. X-ray diffractometry studies exhibit the characteristic reflections of spinel group materials, suggesting that the thermal treatment does not sensibly affect the crystalline structure of the material. A secondary fraction of hematite was also observed. The ferrites exhibit a specific surface area (from BET) of approximately 4 m².g-1. SEM images indicate the material forms agglomerates. As to the magnetic properties, a maximum of 1405.2 Oersted was achieved for the sample treated at 800°C. Mößbauer spectra indicate a fairly low inversion degree in the synthesized materials, which is rather unusual for cobalt ferrite. After deducting the iron fraction present in the form of hematite, there are strong indications that cobalt ferrite was synthesized as a substoichiometric iron-deficient spinel.

Neste trabalho, estudou-se a síntese por sol-gel da ferrita de cobalto (CoFe2O4), variando-se a temperatura de tratamento térmico do xerogel. Nitrato de ferro e nitrato de cobalto foram utilizados como fonte de cátions e ácido cítrico como mineralizador. Os produtos obtidos, tratados a 750, 800 e 850°C, tiveram sua microestrutura e propriedades magnéticas investigadas no intuito de encontrar correlações entre as condições de síntese, as posições ocupadas pelos cátions dentro da estrutura espinélio do composto e as propriedades magnéticas medidas. Estudos de difratometria de raios X exibiram reflexões características da estrutura espinélio, o que sugere que o tratamento térmico não afetou significativamente a estrutura cristalina do material. Uma fração secundária de hematita também foi observada. As ferritas apresentaram área superficial específica (por BET) de aproximadamente 4 m².g-1. Imagens por MEV indicam que o material apresenta-se aglomerado. Quanto às propriedades magnéticas, um máximo de coercividade de 1405.2 Oersted foi encontrado para a amostra tratada a 800°C. Espectros Mößbauer indicaram um baixo grau de inversão nos espinélios formados, o que é incomum para a ferrita de cobalto. Subtraindo do espectro obtido por Mößbauer o excesso de ferro na forma de hematita, há um forte indicativo que a ferrita foi sintetizada de maneira sub-estequiométrica deficiente em ferro. / We herein report a study on the sol-gel synthesis of cobalt ferrite (CoFe2O4) and the effect of treatment temperature on the product outcome. Iron nitrate and cobalt nitrate were used as cation sources and citric acid as mineralizer. Products treated at 750, 800 and 850°C had their microstructure and magnetic properties assessed in order to correlate their synthesis conditions, the positions in which the cations are inserted in the spinel structure and the magnetic behavior displayed by the ferrites. X-ray diffractometry studies exhibit the characteristic reflections of spinel group materials, suggesting that the thermal treatment does not sensibly affect the crystalline structure of the material. A secondary fraction of hematite was also observed. The ferrites exhibit a specific surface area (from BET) of approximately 4 m².g-1. SEM images indicate the material forms agglomerates. As to the magnetic properties, a maximum of 1405.2 Oersted was achieved for the sample treated at 800°C. Mößbauer spectra indicate a fairly low inversion degree in the synthesized materials, which is rather unusual for cobalt ferrite. After deducting the iron fraction present in the form of hematite, there are strong indications that cobalt ferrite was synthesized as a substoichiometric iron-deficient spinel.

Neste trabalho, estudou-se a síntese por sol-gel da ferrita de cobalto (CoFe2O4), variando-se a temperatura de tratamento térmico do xerogel. Nitrato de ferro e nitrato de cobalto foram utilizados como fonte de cátions e ácido cítrico como mineralizador. Os produtos obtidos, tratados a 750, 800 e 850°C, tiveram sua microestrutura e propriedades magnéticas investigadas no intuito de encontrar correlações entre as condições de síntese, as posições ocupadas pelos cátions dentro da estrutura espinélio do composto e as propriedades magnéticas medidas. Estudos de difratometria de raios X exibiram reflexões características da estrutura espinélio, o que sugere que o tratamento térmico não afetou significativamente a estrutura cristalina do material. Uma fração secundária de hematita também foi observada. As ferritas apresentaram área superficial específica (por BET) de aproximadamente 4 m².g-1. Imagens por MEV indicam que o material apresenta-se aglomerado. Quanto às propriedades magnéticas, um máximo de coercividade de 1405.2 Oersted foi encontrado para a amostra tratada a 800°C. Espectros Mößbauer indicaram um baixo grau de inversão nos espinélios formados, o que é incomum para a ferrita de cobalto. Subtraindo do espectro obtido por Mößbauer o excesso de ferro na forma de hematita, há um forte indicativo que a ferrita foi sintetizada de maneira sub-estequiométrica deficiente em ferro. / We herein report a study on the sol-gel synthesis of cobalt ferrite (CoFe2O4) and the effect of treatment temperature on the product outcome. Iron nitrate and cobalt nitrate were used as cation sources and citric acid as mineralizer. Products treated at 750, 800 and 850°C had their microstructure and magnetic properties assessed in order to correlate their synthesis conditions, the positions in which the cations are inserted in the spinel structure and the magnetic behavior displayed by the ferrites. X-ray diffractometry studies exhibit the characteristic reflections of spinel group materials, suggesting that the thermal treatment does not sensibly affect the crystalline structure of the material. A secondary fraction of hematite was also observed. The ferrites exhibit a specific surface area (from BET) of approximately 4 m².g-1. SEM images indicate the material forms agglomerates. As to the magnetic properties, a maximum of 1405.2 Oersted was achieved for the sample treated at 800°C. Mößbauer spectra indicate a fairly low inversion degree in the synthesized materials, which is rather unusual for cobalt ferrite. After deducting the iron fraction present in the form of hematite, there are strong indications that cobalt ferrite was synthesized as a substoichiometric iron-deficient spinel.

Von generellem Interesse für potentielle Anwendungsmöglichkeiten sind Materialien mit speziellen elektrischen bzw. nichtlinearen optischen Eigenschaften. Im Rahmen dieser Arbeit wurden neue dipolare Verbindungen synthetisiert und charakterisiert, welche eine zentrale Organosilanspacereinheit (-SiMex-,-(SiMe2)6-), ein terminales Metallkomplexfragment (potentieller Donor, FcN-) sowie eine terminale organische Akzeptoreinheit (-PhF, -PhBr, -PhCHO) enthalten und gleichzeitig eine große Variationsbreite gewünschter Eigenschaften aufweisen. Aus Photo-EMK-Messungen, UV/VIS-, NMR-Spektroskopie, Mößbauer- und cyclovoltammetrischen Untersuchungen kann auf eine im Festkörper auftretende temperaturabhängig variierende intermolekulare Kopplung zwischen dem Donor und dem organischen Akzeptor geschlossen werden. Photo-EMK- und Einkristallröntgenstrukturanalysen der Salze (Hydrochloride, Pikrate) offenbaren starke intermolekulare Wechselwirkungen (C-H···π, D-C-H···A) mit entscheidendem Einfluß auf Festkörpereigenschaften (supramolekulare MO's).

Von generellem Interesse für potentielle Anwendungsmöglichkeiten sind Materialien mit speziellen elektrischen bzw. nichtlinearen optischen Eigenschaften. Im Rahmen dieser Arbeit wurden neue dipolare Verbindungen synthetisiert und charakterisiert, welche eine zentrale Organosilanspacereinheit (-SiMex-,-(SiMe2)6-), ein terminales Metallkomplexfragment (potentieller Donor, FcN-) sowie eine terminale organische Akzeptoreinheit (-PhF, -PhBr, -PhCHO) enthalten und gleichzeitig eine große Variationsbreite gewünschter Eigenschaften aufweisen. Aus Photo-EMK-Messungen, UV/VIS-, NMR-Spektroskopie, Mößbauer- und cyclovoltammetrischen Untersuchungen kann auf eine im Festkörper auftretende temperaturabhängig variierende intermolekulare Kopplung zwischen dem Donor und dem organischen Akzeptor geschlossen werden. Photo-EMK- und Einkristallröntgenstrukturanalysen der Salze (Hydrochloride, Pikrate) offenbaren starke intermolekulare Wechselwirkungen (C-H···π, D-C-H···A) mit entscheidendem Einfluß auf Festkörpereigenschaften (supramolekulare MO's).