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A análise da Interferência Coulombiana-Nuclear (ICN) foi aplicada à distribuição angular experimental do espalhamento inelástico de 6Li de 28,0 MeV em 76Ge, na excitação do estado 2_1^+. Os dados foram adquiridos no sistema Pelletron-Espectrógrafo Magnético Enge do LAFN do IFUSP. Na detecção dos íons emergentes, no plano focal do imã, foi utilizado um detector sensível à posição (PSD) de barreira de superfície (área de detecção de 47 × 8 mm^2 e espessura útil de 500 m). No presente trabalho foi introduzida a técnica de processamento digital de pulsos (PDP) no sistema de aquisição. Foram medidos espectros associados a vinte e seis ângulos de espalhamento na região angular de interesse: 10^o_Lab 55^o. A análise foi realizada na aproximação de Born com ondas distorcidas (DWBA) utilizando o potencial nuclear de transição descrito pelo modelo do potencial óptico deformado (DOMP) e parâmetros ópticos globais. O ajuste das previsões sobre a distribuição angular experimental foi realizado pela minimização do ^2 através do método iterativo de Gauss. O ajuste permitiu a extração dos parâmetros correlacionados: _2^N, comprimento de deformação nuclear e C_2=(_2^C)(_2^N ), razão entre os comprimentos de deformação de carga e nuclear. Os valores dos parâmetros correlacionados obtidos neste trabalho foram C_2=1,101(20) e _2^N=1,08(21) fm. Testes estatísticos através da simulação de Monte Carlo de 5000 novos conjuntos de dados comprovaram a qualidade do método empregado no ajuste dos parâmetros correlacionados. A metodologia aplicada na análise da ICN, permitiu a extração da razão (B(E2))B(IS2) ,que é proporcional ao quadrado de C_2, com boa precisão devido ao cancelamento da incerteza no fator de escala, das seções de choque absolutas. Os resultados obtidos no presente trabalho são inéditos e permitiram análise da evolução da coletividade ao longo da cadeia de isótopos pares de germânio, em conjunto com os valores obtidos nos isótopos 70,72,74Ge estudados previamente. Os resultados ao longo da cadeia indicaram que, apesar de uma leve predominância da contribuição dos prótons em relação aos nêutrons na excitação dos primeiros estados quadrupolares dos 70,72,76Ge, a contribuição dos nêutrons é consideravelmente maior para o 74Ge. Este aumento sugere forte mistura de configurações na descrição do estado fundamental deste isótopo. / The inelastic scattering of 28,0 MeV 6Li on 76Ge in the excitation of the 2_1^+ state, has been studied with the Coulomb-Nuclear Interference (CNI) analysis. The data were measured at the Pelletron-Enge-Spectrograph facility at LAFN-IFUSP. A solid-state position sensitive silicon detector (PSD) (500 m thickness and 47 × 8 mm^2 area) was used to measure the data at the spectrometer focal plane. Digital pulse processing (DPP) was implemented in the acquisition system. Twenty-six spectra were measured at carefully chosen scattering angles in the range of 10^o_Lab 55^o to obtain an angular distribution. The analysis was performed with the Distorted Wave Born Approximation (DWBA) and applied for the nuclear transition potential, the Deformed Optical Potential Model (DOMP), under well-established global optical parameters. The fit of the predicted cross sections to the experimental data through ^2 minimization, using the iterative method of Gauss, allowed for the extraction of the correlated parameters, _2^N, the mass deformation length, and C_2=(_2^C)(_2^N ), the ratio between charge and mass deformation lengths. The correlated parameters obtained in the present work were C_2=1,101(20) and _2^N=1,08(21) fm. Statistical tests, through a Monte Carlo simulation of 5000 new data sets, validated the method employed in the correlated parameters fit. The methodology applied for the CNI analysis allowed the extraction of ratio(B(EL))(B(ISL)), which is proportional to the square of C_2, with a good precision due to the scale uncertainties cancellation of the absolute cross sections. The values of B(IS2) and of the ratios (B(E2))(B(IS2)) obtained in the present work have not been reported before and allow the study of the evolution of the collectivity throughout the even-A germanium chain together with former results obtained for the 70,72,74Ge isotopes. The results along the chain indicate that although the protons relative to the neutrons reveal a small predominant contribution in 70,72,76Ge to the first quadrupole excitation, the neutron role is strongly enhanced in 74Ge. This behaviour suggests a strong mixing configuration in the 74Ge ground state description

Medidas em coincidência gamma-partícula da reação 7Li+120Sn foram realizadas na faixa de energia de 2.6 a 3.9 MeV por nucleon. Além do canal inelástico, foram observados os canais de pick-up de próton e stripping de um e dois nêutrons, sendo que, para o último caso, cálculos teóricos de DWBA e CRC comparados com o canal elástico demonstram que esta transferência ocorre de maneira sequencial (two-step) e não direta. Este trabalho consolida a existência de canais já anteriormente observados (pick-up de próton e stripping de um nêutron) além de observar pela primeira vez a existência do canal de strippinp de dois nêutrons, no entanto, ele tem um caráter pioneiro pois é o primeiro a medir distribuições angulares de todos esses canais. Tanto o pick-up de próton quanto o stripping de dois nêutrons tiveram de levar em conta na análise cálculos de Monte Carlo que simulassem o efeito da quebra dos projéteis 8Be e 5Li, respectivamente. Fatores espectroscópicos para alguns estados desses canais foram obtidos e são condizentes com os valores esperados considerando o modelo de single particle e a indistinguibilidade de partículas nos casos dos núcleos 119In e 122Sn. Por outro lado, são muito pequenos (ordem de 10e-2) para estados do 121Sn, fato esse gerado pela provável falta de acoplamento de mais canais de reação que reduzem o fluxo da transferência de nêutron. Foram observados também núcleos gerados a partir da transferência seguida de emissão de partículas. / $\\gamma$-particle coincidence measurements of the $^7$Li$+^{120}$Sn reaction were made in the $2.6$ to $3.9$ MeV/nucleon energy range. Besides the inelastic channel, the proton {\\it pick-up} and one/two neutron {\\it stripping} were observed, whereas, for the last case, DWBA and CRC calculations were compared to experimental elastic scattering data and demonstrated that this transfer occurs in a sequential ({\\it two-step}) rather than a direct way. This work consolidates the existence of some channels that have already been observed (proton {\\it pick-up} and neutron {\\it stripping}) and also observes for the first time the existence of the two neutron {\\it stripping} channel, however, it still retains its pioneering as it is the first one to measure the angular distributions for all these channels. The proton {\\it pick-up} and the two neutron {\\it stripping} channels had to take into account in their analysis Monte Carlo calculations to simulate the projectile breaking effect ($^8$Be and $^5$Li, respectively). Spectroscopic factors for some states of these channels were found and are consistent with the expected values considering the {\\it single particle} model and the particle indistinguishability for the $^{119}$In and $^{122}$Sn cases, however, these factors are too small (magnitude order of $10^{-2}$) for the $^{121}$Sn case. This was generated most likely by the lack of coupling of some of the reaction channels that would reduce the one neutron transfer flux. Nuclei generated by the transfer followed by particle emission were also observed.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18067号 / 理博第3945号 / 新制||理||1568(附属図書館) / 30925 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 瀬戸 誠, 教授 鶴 剛, 教授 大久保 嘉高 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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Ferroelectric and ferromagnetic materials have been extensively studied for potential applications in sensors, actuators and transducers. Highly electrostrictive (1-x)Pb(Mg_1/3Nb_2/3)-xPbTiO₃ (PMN-xPT) and highly magnetostrictive Fe-xat.%Ga are two such novel materials. Both materials systems have chemical disorders and structural inhomogeneity on a microscale, giving rise to an interesting diversity of crystal structures and novel macroscopic physical properties, which are dependent on thermal and electrical histories of the crystals. In this thesis, I have to investigated phase transformations in these two systems under thermal and field (electric/magnetic) histories, using x-ray and neutron scattering techniques. In PMN-xPT crystals, x-ray and neutron diffractions were performed along the different crystallographic orientations and for different thermal and electrical histories. Various intermediate monoclinic (M) phases that structurally “bridge” the rhombohedral (R) and tetragonal (T) ones across a morphtropic phase boundary (MPB) have been observed. Systematic investigations of (001) and (110) electric (E) field-temperature phase diagrams of PMN-xPT crystals have demonstrated that the phase stability of PMN-xPT crystals is quite fragile: depending not only on modest changes in E (≤ 0.5kV/cm), but also on the direction along which E is applied. Structurally bridging monoclinic Mc or orthorhombic (O) phases were found to be associated with the T phase, whereas the monoclinic Ma or Mb phases bridged the Cubic (C) and R ones. In addition, neutron inelastic scattering was performed on PMN-0.32PT to study the dynamic origin of the MPB. Data were obtained between 100 and 600 K under various E applied along the cubic [001] direction. The lowest frequency zone-center, transverse optic phonon was strongly damped and softened over a wide temperature range, but started to recover on cooling into the T phase at the Curie temperature (TC). Comparisons of my findings with prior ones for PMN and PMN-0.60PT suggest that the temperature dependence and energy scales of the soft mode dynamics in PMN-xPT are independent of PT concentration below the MPB, and that the MPB may be defined in composition space x when TC matches the temperature at which the soft mode frequency begins to recover. High-resolution x-ray studies then showed that the C–T phase boundary shifted to higher temperatures under E by an expected amount within the MPB region: suggesting an unusual instability within the apparently cubic phase at the MPB. In Fe-xat.%Ga alloys, the addition of Ga atoms into the b.c.c. α-Fe phase also results in diversity of crystal structures and structural inhomogeneity, which are likely the source of its unusual magneto-elastic properties. I have carefully investigated decomposition of Fe-xat.%Ga alloys subjected to different thermal treatments by x-ray and neutron diffraction for 12 < x < 25. Quenching was found to suppress the formation of a DO₃ structure in favor of a high-temperature disordered bcc (A2) one. By contrast, annealing produced a two-phase mixture of A2 + DO₃ for 14 < x < 20 and a fully DO₃ phase for x = 25. A splitting of the (2 0 0) and (0 0 2) Bragg peaks observed along the respective transverse directions indicated that Fe-xat.%Ga –crystals' are composed of several crystal grain orientations (or texture structures), which are slightly tilted with respect to each other. In order to investigate the local structural distortions and heterogeneities, neutron diffuse scattering was performed on Fe-x%Ga alloys for different thermal conditions. Diffuse scattering around a (100) superlattice reflection was found for 14 < x < 22 in the furnace-cooled condition, indicative of short-range ordered DO₃ nanoprecipitates in an A2 matrix. This diffuse intensity had an asymmetric radial contour and an off-centering. Analysis (x=19) revealed two broad peaks with c/a–1.2: indicating that the DO₃-like nanoprecipitates are not cubic, but rather of lower symmetry with a large elastic strain. The strongest diffuse scattering was observed for x=19, which correspondingly had maximum magnetostriction: indicating a structural origin for enhanced magnetostriction. / Ph. D.

Growing environmental concerns, coupled with increasing regulatory restrictions, are requiring industries to develop non-lead-based compositions of ferroelectric and piezoelectric materials. These materials—now widely used in sensors, actuators, and transducers—are for the most part lead-based compounds such as Pb(Zr,Ti)O₃ (PZT). Indeed, PZT represents the dominant market share for use in these technologies. Moreover, next generation compounds, which include Pb(Mg_1/3Nb_2/3)O₃-xat%PbTiO₃ (PMN-x%PT) crystals with ultrahigh piezo-/electromechanical properties, are also Pb-based systems and thus are problematic for meeting more restrictive environmental standards. As alternative, Pb-free ferroelectrics such as NBT-derived single crystals represent viable next-generation materials for use in ferro-/piezoelectric applications. Development of these types of NBT-based crystals has made important advancements in the last decade. In fact, the performances of NBT-based materials are beginning to approach the properties of the widely used commercial PZT ceramic material. Nonetheless, additional studies are needed before it being able to compete with PMN-x%PT and PZN-x%PT crystals in next-generation applications. As a new type of piezoelectric material, much remains to be learned about Pb-free piezoelectric crystals. For instance, in addition to enhancing our understanding the nature of the piezoelectric third-rank tensor coefficients such as d₃₃ and d₁₅, a thorough knowledge of the Curie temperature, leakage current, and electromechanical properties is also essential for increasing the applications potential of these crystals. As detailed herein, multiple dopants may have to be incorporated into NBT to modify its microstructure and properties to meet these specific requirements, which may further complicate its chemical structure-property relationships. This study, therefore, was designed to investigate the heterogeneous structure of NBT-based single crystals, using x-ray diffraction, transmission electron microscopy, and neutron inelastic scattering, with the goal of investigating the mechanism coupling of morphotropic phase boundary (MPB) and the maximum property responses in A-site disordered perovskite Pb-free piezoelectric systems. Using the framework of polar nanoregions and adaptive phase theory, I sought to determine how the nanostructure of these single crystals change with temperature and composition—and how these factors impact its properties. Diffuse scattering, domain morphology, and phonon dispersions were used to investigate both the static and dynamic properties of these heterogeneous structures. / Ph. D. / Growing environmental concerns, coupled with increasing regulatory restrictions, are requiring industries to develop non-lead-based compositions of ferroelectric and piezoelectric materials. These materials—now widely used in sensors, actuators, and transducers—are for the most part lead-based compounds such as Pb(Zr,Ti)O₃ (PZT). Indeed, PZT represents the dominant market share for use in these technologies. Moreover, next generation compounds, which include Pb(Mg_1/3Nb_2/3)O₃-xat%PbTiO₃ (PMN-x%PT) crystals with ultrahigh piezo- /electromechanical properties, are also Pb-based systems and thus are problematic for meeting more restrictive environmental standards. As alternative, Pb-free ferroelectrics such as (Na_1/2Bi_1/2)TiO₃ (NBT) -derived single crystals represent viable next-generation materials for use in ferro-/piezoelectric applications. Development of these types of NBT-based crystals has made important advancements in the last decade. In fact, the performances of NBT-based materials are beginning to approach the properties of the widely used commercial PZT ceramic material. Nonetheless, additional studies are needed before it being able to compete with PMN-x%PT and PZN-x%PT crystals in next-generation applications. As a new type of piezoelectric material, much remains to be learned about Pb-free piezoelectric single crystals. In addition to enhancing our understanding the nature of the piezoelectric properties, increasing the applications potential of these crystals is also essential. And these specific requirements from different applications further push the researchers to find a more effective model to lead the piezoelectric single crystals growth as well as developments. This study, therefore, was designed to investigate the unique microstructure of NBTbased single crystals, using x-ray diffraction, transmission electron microscopy, and neutron inelastic scattering, with the goal of investigating the mechanism coupling between the chemical compositions and the maximum property responses in these specific Pb-free piezoelectric systems. Using the framework of an advanced microstructure description model, I sought to determine how the nanostructure of these single crystals change with temperature and composition—and how these factors impact its properties. The results from different experiment methods also successfully supported each other and brought new perspectives to the Pb-free material researches.

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No description available.

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