In dieser Arbeit wurde die Kupferoxidebene des Hochtemperatur - Supraleiters Yttrium- Barium-Kupferoxid (YBa2Cu3O6+y) mit Hilfe von Kernmagnetischer-Resonanz (NMR - nucleus magnetic resonance) unter Drücken von bis zu 4.4GPa untersucht. Es wurden 2 dieser Druckzellen gebaut, sie enthielten verschieden stark dotierte Einkristalle. Die Änderungen der Ladungsverteilungen in der Kupferoxidebene abhängig von der Dotierung und vom Druck lagen hierbei im Fokus der Untersuchungen. Motivation dieser Arbeit war es YBa2Cu3O6+y Einkristalle bei höheren Drücken als zuvor mit NMR zu untersuchen. Dabei wurde der alte Rekord von 1.8GPa (Steven Reichardt 2018) auf 4.4GPa erhöht (aktuelle Arbeit). Da sich die Probenkammer in einer Druckzelle stark verformt, muss die Unversehrtheit der Kristalle an jedem Druckpunkt überprüft werden. Dies wurde unter anderem mit Bildern,welche mit dem Mikroskop durch die transparenten Anvils gemacht wurden, überprüft, als auch durch aufwendige Höhenmessungen der Probenkammer mit speziellen Mikroskopen in Verbindung mit einem Piezo-gesteuertem Probentisch. Durch die exakte Vermessung und Positionierung der Einkristalle auf dem Anvil konnte in Verbindung mit den Höhen- und Druchmessermessungen sichergestellt werden, dass sich der Kristall unter hydrostatischen Druckbedingungen befindet und nicht linear entlang der Zellenachse komprimiert wird, was zu einem Brechen oder einer Veränderung der Orientierung hätte führen können. Eine allgemeine Erkenntnis konnte dabei gewonnen werden, über die Stabilität, insbesondere der Höhe der Probenkammer, welche zunimmt mit dem Durchmesser des Culets. Dies ist entgegen des allgemeinen Prinzipes der Miniaturisierung zum erreichen höherer Drücke, für die Planung der Zellenarchitektur für Einkristallmessungen in NMR-Anvilzellen aber wichtig. Weiterhin mussten auch andere wichtige Parameter für NMR Messungen erfüllt werden. Die Architektur der Mikrospule welche in der Probenkammer um den Kristall gelegt wurde, mussten um den Füllfaktor zu maximieren an die Dimensionen der Kristalls angepasst werden. Dazu wurde eine Methode entwickelt um elliptische Mikrospulen von Hand zu wickeln, darin wurden die flachen Kristalle aufrecht platziert. Damit konnte das Signal auf eine annehmbare Intensität gebracht werden um in endlicher Zeit Messungen realisieren zu können. Mit den Messungen an Yttrium-Barium-Kupferoxid Einkristallen unter Druck konnte gezeigt werden, dass mit steigendem Druck sowohl die zunehmende Dotierung der Kupferoxidebene die Position am Sauerstoffatom bevorzugt, als auch eine Ladungsumverteilung in der Kupferoxidebene induziert wird. Weiterhin wurden NMR-Messungen am Indium Kern des Thermoelektrika Silber-Indium-Tellurid unter Druck durchgeführt. 5 verschiedenen Druckzellen wurden gebaut und bei Drücken bis zu 10GPa wurde gemessen. Bis 2.5GPa konnten Spektren aufgezeichnet werden die einen Anstieg des elektrischen Feldgradienten nahelegten. Dieser anstiegt konnte mit Nutationsexperimenten bestätigt werden. Die Echo-Experimente bei 4GPa und 5GPa wiesen einen starken Signalverlust auf und legten eine Quadropolaufspaltung des Zentralübergangs zweiter Ordnung nahe. Über 5GPa wurde kein Signal mehr gefunden. Nach dem Ablassen des Drucks zurück zu Umgebungsbedingungen wurde wieder ein Signal bei der ursprünglichen Frequenz gemessen.:0 Introduction 1 Theoretical Basics, Page 5 1.1 Nuclear Magnetic Resonance (NMR), Page 6 1.2 NMR Setup, Page 14 1.3 Pressure as Parameter, Page 17 1.4 NMR under Pressure, Page 28 2 Samples, Page 31 2.1 Yttrium-Barium-Copper-Oxide, Page 32 2.2 Silver-Indium-Telluride, Page 42 3 Experimental, Page 45 3.1 Spectrometer and Magnet, Page 46 3.2 Evaluation of the Measured Signals,Page 46 3.3 Micro Electronics, Page 47 3.4 Summary of the Chapter, Page 53 4 Sample Chamber Monitoring for single crystal NMR in high pressure cells, Page 55 4.1 Necessity of Sample Chamber Monitoring, Page 56 4.2 Measurements, Page 57 4.3 error consideration, Page 64 4.4 Discussion, Page 65 5 Single Crystal NMR of YBa2Cu3O6+y up to 4.4 GPa, Page 67 5.1 Doping Level and the Critical Temperature, Page 68 5.2 Orientation of the Single Crystal, Page 73 5.3 Discussion, Page 81 6 Silver-Indium-Telluride NMR under pressure, Page 83 6.1 Introduction, Page 84 6.2 Sample, Page 85 6.3 Pressures Cells, Page 85 6.4 Measurments, Page 87 6.5 Discussion, Page 97 7 Summary and Outlook, Page 99 7.1 Summary, Page 100 7.2 Conclusion and Outlook, Page 103 Appendix A Appendix, Page 107 A.1 Spectra, Page 108 Y-6.85 Cell, Page 108 Y-6.5 Cell, Page 113 References 127 / In this work the CuO2-plane of the high temperature superconductor yttrium-bariumcopper-oxide (YBa2Cu3O6+y) is investigated by nuclear magnetic resonance (NMR) under pressures up to 4.4GPa. Two high pressure NMR cells were built and filled with differently doped single crystals. The changes of the charge distribution in the CuO2-plane depending on doping and depending on pressure were the focus of the investigations. The motivation of this work was to extend the NMR measurements of YBa2Cu3O6+y single crystals in NMR anvil cells with pressures not achieved before. The old record (from Steven Reichardt 2018) of YBa2Cu3O6+y single crystals up to 1.8GPa was increased to 4.4GPa with this work. Due to the large deformation of the sample chamber, the integrity of a single crystal has to be checked at every pressure point. This was done by pictures, shot through the transparent anvils as well as height measurements of the sample chamber with a special microscope combined with a piezo controlled table. The exact measurements of the position of the single crystals as well as the height and diameter measurements assured that the single crystal is still in hydrostatic conditions or if it is tilted or pressurized linearly. A general cognizance about the stability of the sample chamber was acquired, especially about the stability of the height, which increases with the diameter of the culet. This is contrary to the general principle of miniaturization to reach higher pressures, if single crystals are of interest. The aim here is to have a stable sample chamber for good measuring conditions for NMR under pressure. Further, other expectations for the parameters of a NMR experiment had to be fulfilled as well. The architecture of a microcoil, which is placed around the crystal in the chamber, had to match the flat crystal shape to increase the filling factor and with this the signal to noise ratio (SNR) of the probe. For this, a method to wind elliptical micro coils by hand under the microscope was developed. Thereby signal intensity could be increased to an acceptable value which allowed more rapid measurements. With the measurements on YBa2Cu3O6+y single crystals under pressure it was shown that increasing pressure increase the hole doping in the CuO2-plane. Furthermore a redistibution of the charges in the CuO2-plane occurs. In a second part of this thesis 115In NMR measurements on the thermoelectric AgInTe2 under pressure up to 10GPa in 5 different cells were preformed. Up to 2.5GPa spectra were recorded which could be explained by an increase of the quadrupole frequency. This increase was verified by a power dependent nutation spectroscopy experiment. The echo experiments of pressures between 3GPa and 5GPa showed a high signal loss and pointed to an increasing disorder and a second order affected central transition of a powder spectrum. No signal was found above 5GPa despite elaborate searches in particular for a possible metallic component. After the pressure release a signal was found again at ambient conditions frequency.:0 Introduction 1 Theoretical Basics, Page 5 1.1 Nuclear Magnetic Resonance (NMR), Page 6 1.2 NMR Setup, Page 14 1.3 Pressure as Parameter, Page 17 1.4 NMR under Pressure, Page 28 2 Samples, Page 31 2.1 Yttrium-Barium-Copper-Oxide, Page 32 2.2 Silver-Indium-Telluride, Page 42 3 Experimental, Page 45 3.1 Spectrometer and Magnet, Page 46 3.2 Evaluation of the Measured Signals,Page 46 3.3 Micro Electronics, Page 47 3.4 Summary of the Chapter, Page 53 4 Sample Chamber Monitoring for single crystal NMR in high pressure cells, Page 55 4.1 Necessity of Sample Chamber Monitoring, Page 56 4.2 Measurements, Page 57 4.3 error consideration, Page 64 4.4 Discussion, Page 65 5 Single Crystal NMR of YBa2Cu3O6+y up to 4.4 GPa, Page 67 5.1 Doping Level and the Critical Temperature, Page 68 5.2 Orientation of the Single Crystal, Page 73 5.3 Discussion, Page 81 6 Silver-Indium-Telluride NMR under pressure, Page 83 6.1 Introduction, Page 84 6.2 Sample, Page 85 6.3 Pressures Cells, Page 85 6.4 Measurments, Page 87 6.5 Discussion, Page 97 7 Summary and Outlook, Page 99 7.1 Summary, Page 100 7.2 Conclusion and Outlook, Page 103 Appendix A Appendix, Page 107 A.1 Spectra, Page 108 Y-6.85 Cell, Page 108 Y-6.5 Cell, Page 113 References 127

This licentiate thesis presents developments of nanocalorimetry systems tailored for use under extreme conditions such as high pressure, intense magnetic fields, and low temperature. Nanocalorimetry is a powerful approach to study strongly correlated systems like superconductors, heavy fermions, and quantum materials with non-trivial magnetic or electronic properties, materials with emergent magnetic orders, as well as quasicrystals. Introducing high pressure or magnetic fields as tuning parameters in specific heat measurements at low temperatures can enhance the understanding of underlying physical properties of such materials. The key component of calorimeters is the thermometer. A thin-film thermometer based on a composite ceramic metal oxide has been developed. It shows high sensitivity and negligible magnetoresistance over a broad temperature range. Two different nanocalorimeters are fabricated starting from an existing nanocalorimeter design, a high-pressure nanocalorimeter and a calorimeter for sample rotations in high magnetic fields. The high-pressure nanocalorimetry setup involves a nanocalorimeter built on a robust substrate combined with a diamond anvil cell, a gasket sandwich with electric leads, and an optical setup for pressure detection through ruby fluorescence spectroscopy. The high-field nanocalorimeters are fabricated on SiNx membranes for specific heat measurements down to 30 mK. Miniaturization is performed to extend their use for angular-dependent measurements in high magnetic fields, so far used up to 41 T. Reducing the calorimeter platform size in both calorimeters is achieved by a method of plasma etching performed after device fabrication. Specific heat measurements of Eu-doped GdCd7.88 quasicrystals and GdCd6 approximant systems are performed in fields up to 12 T. The preliminary results show the presence of spin-glass behavior in the quasicrystals and an antiferromagnetic transition in the approximant crystals at low temperatures.

No description available.

Mechanical pressure offers unique control over the energy landscape of chemical reactions, opening up pathways that are inaccessible through conventional thermochemistry. We hypothesize that the reduced dimensionality defines the conformational space of the high-pressure reaction, giving rise to new selectivity that is unavailable in 3D systems. Here, we demonstrate this concept through the pressure-controlled topochemical polymerization of the diacetylene molecule deca‐3,5‐diyn‐1‐amine (DDA) incorporated in the two-dimensional (2D) perovskite [DDA]2PbBr4. Compression at 3 GPa drives the first topochemical polymerization through 1,2 addition, forming a polyene product at room temperature. The reaction is initiated by the mechanical bending of the linear DDA molecule, a mechanism fundamentally different from the 1,4-addition in 3D solids. Importantly, pressure hinders the second 1,2-addition by disfavoring the gauche conformation between the remaining acetylene groups, allowing for the selective formation of polyene versus polyacene products. We characterize the reaction mechanisms and products using spectroscopies (Raman, X-ray photoelectron, ultraviolet-visible), X-ray diffraction and density-functional theory simulations. These results highlight the important role of dimensionality in high-pressure chemistry, and offers a new paradigm for creating low-dimensional functional materials.

Physics at extreme conditions is not a young field; there have been decades of developments that have allowed us to generate high-pressure and high-temperature conditions in a vast array of materials. Conventionally, these extreme conditions were generated using static compression techniques; compressing a material in a diamond anvil cell which could then be heated or cooled, with structural information deduced using synchrotron radiation. These techniques are still invaluable for extreme conditions research although the pressures and temperatures that are accessible to them are limited by the strength of the diamond anvil cells and their ability to withstand extreme temperatures. The necessity for access to pressure-temperature states that are beyond the scope of the conventional diamond anvil cell is driven by the need to characterise extreme environments such as planetary interiors. It was long believed that materials in high pressure-temperature states would exhibit relatively simple, high-symmetry crystal structures, but recent research has proven that, conversely, there is an abundance of complex structural behaviour at these extreme conditions. One means of attaining pressure-temperature states beyond those accessible using static compression techniques is to impart a large amount of energy into a material in a comparatively short period of time (milliseconds to nanoseconds); this is known as dynamic compression. Dynamic compression can be generated using impact techniques or, alternatively, via laser ablation. Access to the most extreme conditions is commonly achieved by generating a shockwave which compresses the sample with the fastest achievable compression wave. Not only does this type of compression facilitate access to the most extreme states, it also allows us to explore the physics of impact phenomena and other such situations involving rapid energy transfer. Dynamic compression occurs on short timescales and, as such, there is a considerable challenge in implementing diagnostics to study the behaviour of compressed materials. Furthermore, because complexity is commonplace in extreme conditions, it is vital that any diagnostics should be able to provide data of high enough quality that this complexity may be resolved. The advent of 4th generation light sources (x-ray free electron lasers) has afforded us the opportunity to obtain extraordinarily high quality data on dynamic compression timescales. In the interest of refining analytical techniques when utilising this novel technology, materials exhibiting complex crystal structures should be investigated. Antimony is an element which is known, under static compression, to transform from a Peierls-distorted rhombohedral phase (R-3m) to an incommensurately modulated host-guest structure (I'4=mcm(00γ)000s), a structure with an incredibly high level of complexity. The complexity of this host-guest phase, and the relatively low pressure at which it forms, makes antimony an ideal candidate for testing the resolution achievable using these 4th generation light sources. Furthermore, it is interesting to observe whether such a complex phase can form on the short timescales of dynamic compression. In this work antimony is both statically and dynamically compressed and the results of both experiments are compared. A static phase diagram is constructed for antimony up to 31 GPa and 835 K, confirming the location of a previously theorised triple point and suggesting the location of an additional triple point. Three solid phases are characterised and data are found to agree with the pre-existing static compression studies. The nature of the host-guest phase is investigated and the guest 'chains' are found to remain intact even at the highest temperatures and pressures, a result which has not previously been observed in high pressure-temperature host-guest structures. Dynamic data from shock-compression experiments at pressures up to 59.3 GPa are plotted alongside the static data and contrasting phase behaviour is discussed. Four solid phases are identified along with one liquid phase. Observation of the host-guest phase in shock-compressed antimony confirms that highly complex crystal structures are able to form on the nanosecond timescale.

<p>This thesis presents transverse magnetoresistance (MR) and Hall resistivity measurements of nickel thin films at temperatures between 280 and 455 K and pressures up to 6 GPa. An experimental system was developed for conducting precise magnetotransport measurements using the current reversal and van der Pauw techniques in combination with a 10 T superconducting magnet. Polycrystalline Ni_0.985O_0.015 thin film samples were manufactured with preexisting point contacts allowing highly reproducible magnetotransport measurements at pressure in the diamond anvil cell (DAC).</p><p>The magnetic resistivity above the technical saturation of the magnetization was found to decrease linearly to the highest applied fields, 10 T, while the field derivative, 0.010-0.018 µΩ cm T^-1 between 280 and 316 K, increased with temperature and decreased with pressure. The decrease in the magnetoresistance is attributed to spin wave damping of electron-magnon scattering processes at high fields. The magnon mass, 535(14) meV Ų at 0 K and 0 GPa, determined from longitudinal magnetic resistivity theory is a slightly increasing function of pressure. Correlation between the zero field resistivity and the extraordinary Hall coefficient (EHC) confirmed side jump scattering as the dominant diffusion mechanism at 0 GPa, however, skew scattering was found to become increasingly important with pressure.</p><p>The effect of oxygen and pressure on the density of states (DOS) at the Fermi level was investigated through total energy band structure calculations using a periodic supercell of 64 atoms to simulate the sample chemistry. The DOS of Ni_0.985O_0.015 at the Fermi level was found to increase by 27% at 10 GPa relative to 0 GPa. However, when compared to the results for pure Ni, decreases of 60% and 23% occurred for the corresponding calculations at 0 and 10 GPa. The relative differences in the magnetic resistivity are attributed to competing effects between the DOS, average magnetic moment and magnon mass.</p><p>The technique developed for conducting magnetotransport measurements at pressure is applicable to the study of electronic diffusion in ferromagnets as well as geophysical problems such as the geodynamo.</p>

This thesis presents transverse magnetoresistance (MR) and Hall resistivity measurements of nickel thin films at temperatures between 280 and 455 K and pressures up to 6 GPa. An experimental system was developed for conducting precise magnetotransport measurements using the current reversal and van der Pauw techniques in combination with a 10 T superconducting magnet. Polycrystalline Ni0.985O0.015 thin film samples were manufactured with preexisting point contacts allowing highly reproducible magnetotransport measurements at pressure in the diamond anvil cell (DAC). The magnetic resistivity above the technical saturation of the magnetization was found to decrease linearly to the highest applied fields, 10 T, while the field derivative, 0.010-0.018 µΩ cm T-1 between 280 and 316 K, increased with temperature and decreased with pressure. The decrease in the magnetoresistance is attributed to spin wave damping of electron-magnon scattering processes at high fields. The magnon mass, 535(14) meV Å2 at 0 K and 0 GPa, determined from longitudinal magnetic resistivity theory is a slightly increasing function of pressure. Correlation between the zero field resistivity and the extraordinary Hall coefficient (EHC) confirmed side jump scattering as the dominant diffusion mechanism at 0 GPa, however, skew scattering was found to become increasingly important with pressure. The effect of oxygen and pressure on the density of states (DOS) at the Fermi level was investigated through total energy band structure calculations using a periodic supercell of 64 atoms to simulate the sample chemistry. The DOS of Ni0.985O0.015 at the Fermi level was found to increase by 27% at 10 GPa relative to 0 GPa. However, when compared to the results for pure Ni, decreases of 60% and 23% occurred for the corresponding calculations at 0 and 10 GPa. The relative differences in the magnetic resistivity are attributed to competing effects between the DOS, average magnetic moment and magnon mass. The technique developed for conducting magnetotransport measurements at pressure is applicable to the study of electronic diffusion in ferromagnets as well as geophysical problems such as the geodynamo.

Elastic properties of the major constituent minerals in the Earth’s upper mantle at relevant high pressure-temperature (P-T) conditions are crucial for understanding the composition and seismic velocity structures of the region. In this study, we have measured the single-crystal elasticity of natural Fe-bearing pyrope, Mg2.04Fe0.74Ca0.16Mn0.05Al2Si3O12, using in situ Brillouin spectroscopy and X-ray diffraction at simultaneous high P-T conditions up to 20 GPa and 750 K in an externally-heated diamond anvil cell. The derived aggregate adiabatic bulk and shear modulus (KS0, G0) at ambient conditions are 168.2 (±1.8) GPa and 92.1 (±1.1) GPa, respectively, consistent with literature results. Using the third-order Eulerian finite-strain equation to fit the high P-T data, the derived pressure derivative of the bulk and shear moduli at constant temperature are (∂KS/∂P)T=4.4 (±0.1) and (∂G/∂P)T=1.2 (±0.1), respectively. Applying these pressure derivatives, the temperature derivative of these moduli at constant pressure are also calculated, yielding (∂KS/∂T)P=-18.5(±1.3) MPa/K and (∂G/∂T)P=-5.2(±1.1) MPa/K, respectively. Compared to literature values, our results show that addition of 25% Fe in pyrope increases the pressure derivative of the bulk modulus by 7%, but has a negligible effect on other elastic parameters. Extrapolation of our results shows that Fe-bearing pyrope remains almost elastically isotropic at relevant P-T conditions of the upper mantle, indicating that it may not have a significant contribution to seismic Vp and Vs anisotropy in the upper mantle. Together with the elasticity of olivine and pyroxene minerals in the upper mantle, we have constructed new velocity profiles for two representative compositional models, pyrolite and piclogite, along Earth’s upper mantle geotherm. These velocity models show Vs profiles consistent with seismic observations, although Vp profiles are slightly lower than in seismic models. / text

The presented thesis focuses on study of transport and thermoelastic properties of materials under conditions of planetary interiors by means of high-pressure experimental tools and finite element modeling, and their role in the dynamics and states of cores of terrestrial planets. Experiments in laser-heated diamond anvil cell (LHDAC) in combination with numerical simulations of heat transfer in DAC are shown to yield information on thermal conductivity of a pressurized sample. The novel technique consists of one-sided laser heating and double-sided temperature measurements and utilizes a precise determination of several parameters in course of the experiment, including the sample geometry, laser beam power distribution, and optical properties of employed materials. The pressure-temperature conditions at the probed portion of the sample are, however, not uniform. To address this problem, thermal pressure in the laser-heated diamond anvil cell and anisotropic thermal conductivity originating from the texture development upon uniaxial compression have been studied by means of numerical simulations. The method for determination of thermal conductivity is applied to iron at pressures up to 70 GPa and temperatures of 2000 K, meeting the Earth’s lower mantle conditions and covering Mercury’s entire core. The obtained results are extrapolated to the conditions of the Earth’s core-mantle boundary using a theoretical model of the density dependence of thermal conductivity of metals and published values on Grüneisen parameter and bulk modulus. After considering the effect of minor core elements, the obtained value at these conditions supports case for the downward revision of the thermal conductivity in the core. From the point of view of core dynamics and energy budget, the lower thermal conductivity implies more favorable conditions to drive the dynamo. Similar scenario applies for Mercury where, for high values of thermal conductivity, heat flux conducted along the iron-core adiabat exceeds the actual heat flux through the core-mantle boundary. This leads to a negative rate of entropy production in the core that makes it impossible to sustain the dynamo process presumably responsible for the observed magnetic field of Mercury.

Transition metals (Ti, Zr, Hf, Mo, W, V, Nb, Ta, Pd, Pt, Cu, Ag, and Au) are essential building units of many materials and have important industrial applications. Therefore, it is important to understand their thermal and physical behavior when they are subjected to extreme conditions of pressure and temperature. This dissertation presents: An improved experimental technique to use lasers for the measurement of thermal conductivity of materials under conditions of very high pressure (P, up to 50 GPa) and temperature (T up to 2500 K). An experimental study of the phase relationship and physical properties of selected transition metals, which revealed new and unexpected physical effects of thermal conductivity in Zr, and Hf under high P-T. New phase diagrams created for Hf, Ti and Zr from experimental data. P-T dependence of the lattice parameters in α-hafnium. Contrary to prior reports, the α-ω phase transition in hafnium has a negative dT/dP slope. New data on thermodynamic and physical properties of several transition metals and their respective high P-T phase diagrams. First complete thermodynamic database for solid phases of 13 common transition metals was created. This database has: All the thermochemical data on these elements in their standard state (mostly available and compiled). All the equations of state (EoS) formulated from pressure-volume-temperature data (measured as a part of this study and from literature). Complete thermodynamic data for selected elements from standard to extreme conditions. The thermodynamic database provided by this study can be used with available thermodynamic software to calculate all thermophysical properties and phase diagrams at high P-T conditions. For readers who do not have access to this software, tabulated values of all thermodynamic and volume data for the 13 metals at high P-T are included in the APPENDIX. In the APPENDIX, a description of several other high-pressure studies of selected oxide systems is also included. Thermophysical properties (Cp, H, S, G) of the high P-T ω-phase of Ti, Zr and Hf were determined during the optimization of the EoS parameters and are presented in this study for the first time. These results should have important implications in understanding hexagonal-close-packed to simple-hexagonal phase transitions in transition metals and other materials.