20 research outputs found
Experimental studies of the medical radioisotopes production in neutron spectra generated by 660 MeV protons and 1-8 GeV deuterons in massive uranium target
No full textFINE STRUCTURE OF BETA-DECAY STRENGTH FUNCTION AND ANISOTROPY OF ISOVECTOR NUCLEAR DENSITY COMPONENT OSCILLATIONS IN DEFORMED NUCLEI
No full textTemperature dependence of the pyro- and photoelectric response in Sn/sub 2/P/sub 2/S/sub 6/ films
No full text
Multilayered ceramic heterostructures of lead zirconate titanate and nickel-zinc ferrite for magnetoelectric sensor elements
No full textNew Electron Conversion Lines from Existing ?-Transitions In 160dy
No full textThree photo plates derived with spectrograph LNP JINR with constant magnetic field [1] have been investigated using the Microscope Automatic Scanning MAS [2]. Electron internal conversion (ICE) spectrograms of two erbium (Er P-2, Er P-8) and one Ho fractions has been measured. More detailed analysis gave us the possibility to obtain some new lines (see table) in addition to many earlier existing lines in 160Dy [3]. For that investigations it is necessary to increase the speed with which microscopic objects are measured are described. These efforts include the modernization of the MAS automatic scanning microscope and the development of programs to reach an initial point and for carrying out automatic point-to-point linear transitions with a specified step. The error in realizing a transition to a given point with specified coordinates is shown to amount to 1 µm
A study of non-elastic reaction rates for the ADS materials in the environment of spallation neutrons produced by 1.6GeV d-beam
No full textExperimental determination of residual nuclei formation cross sections in 660 MeV proton reactions with 239Pu and natU
No full textThe paper gives an information about part of the investigations held in JINR Dubna within cooperation of several research institutions and universities. Experimental cross sections for proton induced reactions of an energy of 660 MeV with various fission products, minor actinides, and "major" actinides (plutonium, uranium, thorium) are studied. The paper describes 239Pu and natU experiments; other experiments have already been published or are planned for the time being. Cross section determination consist of three parts: experiment, data processing, and mathematical codes simulation of the problem. This paper deals only with experiment description and data processing methodology. Neither final results of processing, nor simulation of plutonium experiment are paper-ready at the moment. Uranium data have partially already been presented, final complete results are planned to be published with plutonium results together in reviewed journal
Исследование сегнетоэлектрических нанокомпозитов на основе P(VDF-TrFE) методами сканирующей зондовой микроскопии
No full textCeramic and polymer based nanocomponents combine the properties of their constituents, e.g. flexibility, elasticity, polymer reprocessability, hardness typical of glass, wear resistance and high light refraction index. This helps improving many properties of the materials in comparison with the source components. Since recently researchers have been manifesting interest to the properties of complex composite compounds. This is primarily caused by the unique properties of their structures as compared with conventional materials having homogeneous composition. Secondly, this interest is caused by the fact that these compounds may prove to be much cheaper than homogeneous structures provided the physical properties of the composite in a preset range of parameters (temperature, applied field frequency etc.) are identical to those of the respective homogeneous materials. For example, polyvinyl idenfluoride (PVDF) type ferroelectric polymers and copolymers on its basis have found wide application for functional elements of various electromechanic devices in advanced electronics due to their relatively good piezoelectric and pyroelectric properties. The strong random polarization and the formation of polar non-centrosymmetric crystals provide for the high piezoelectric and pyroelectric activity in these crystals. Scanning probe microscopy has been used for study of ferroelectric nanocomposites having different compositions. The matrix specimen for study of local polarization switching at a nanoscale level was vinyl idenfluoride and trifluoroethylene P(VDF-TrFE) copolymer possessing sufficiently high crystallinity. The composite fillers were barium titanate BaTiO3 and deuterized triglycinsulfate DTGS ferroelectric powders and zirconate-titanate lead barium BPZT ceramic powder. We show these materials to show good promise for use in memory cells.Нанокомпозиты на основе керамики и полимеров сочетают в себе качества составляющих их компонентов: гибкость, упругость, перерабатываемость полимеров и характерные для стекол твердость, устойчивость к износу, высокий показатель светопреломления. Благодаря этому улучшаются многие свойства материалов по сравнению с исходными компонентами. В последнее время исследователи проявляют большой интерес к изучению свойств сложных композитных соединений. Во-первых, это связано с уникальными свойствами таких структур по сравнению с «обычными», однородными по составу веществами. Во-вторых, — с тем, что подобные соединения могут оказаться значительно более дешевыми, чем однородные структуры, при условии, что композит по ряду физических показателей и в диапазоне заданных параметров (температуры, частоты приложенного поля и т.д.) идентичен однородным веществам. Так, сегнетоэлектрические полимеры типа поливинилиденфторида (PVDF) и сополимеры на его основе нашли широкое применение в качестве функциональных элементов различных электротехнических устройств в современной электронике за счет своих относительно высоких пьезоэлектрических и пироэлектрических свойств. Высокая спонтанная поляризация и образование полярных нецентросимметричных кристаллов обуславливают появление в этих материалах высокой пьезо- и пироактивности. Методами сканирующей зондовой микроскопии исследованы сегнетоэлектрические нанокомпозиты различных составов. В качестве образца-матрицы для исследования локального переключения поляризации на наномасштабе был выбран сополимер винилиденфторида с трифторэтиленом P(VDF-TrFE), обладающий достаточно высокой долей кристалличности. В качестве наполнителя для композита выбраны порошки сегнетоэлектриков титаната бария BaTiO3 и дейтерированного триглицинсульфата DTGS, керамический порошок цирконата-титаната бария свинца BPZT. Показано, что эти материалы являются перспективными для использования в качестве элементов памяти.
Microscopia de força piezoeléctrica de relaxors ferroeléctricos
No full textDoutoramento em Ciência e Engenharia de MateriaisNesta tese, ferroeléctricos relaxor (I dont know uf the order is correct) de base
Pb das familias (Pb,La)(Zr,Ti)O3 (PLZT), Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT),
Pb(Zn1/3,Nb2/3)O3-PbTiO3 (PZN-PT) foram investigados e analisados. As
propriedades ferroeléctricas e dieléctricas das amostras foram estudadas por
métodos convencionais de macro e localmente por microscopia de força
piezoeléctrica (PFM).
Nos cerâmicos PLZT 9.75/65/35 o contraste da PFM à escala nanometrica _
foi investigado em função do tamanho e orientação dos grãos. Apurou-se que
a intensidade do sinal piezoeléctrico das nanoestruturas diminui com o
aumento da temperatura e desaparece a 490 K (La mol. 8%) e 420 K (9,5%).
Os ciclos de histerese locais foram obtidos em função da temperatura. A
evolução dos parâmetros macroscópicos e locais com a temperatura de
superfície sugere um forte efeito de superfície nas transições de fase
ferroeléctricas do material investigado. A rugosidade da parede de domínio é
determinada por PFM para a estrutura de domínio natural existente neste
ferroeléctrico policristalino. Além disso, os domínios ferroeléctricos artificiais
foram criados pela aplicação de pulsos eléctricos à ponta do condutor PFM e o
tamanho de domínio in-plane foi medido em função da duração do pulso.
Todas estas experiências levaram à conclusão de que a parede de domínio
em relaxors do tipo PZT é quase uma interface unidimensional. O mecanismo
de contraste na superfície de relaxors do tipo PLZT é medido por PFMAs estruturas de domínio versus evolução da profundidade foram estudadas
em cristais PZN-4,5%PT, com diferentes orientações através da PFM. Padrões
de domínio irregulares com tamanhos típicos de 20-100 nm foram observados
nas superfícies com orientação das amostras unpoled?. Pelo contrário,
os cortes de cristal exibem domínios regulares de tamanho mícron
normal, com os limites do domínio orientados ao longo dos planos
cristalográficos permitidos. A existência de nanodomínios em cristais com
orientação está provisoriamente (wrong Word) atribuída à natureza
relaxor de PZN-PT, onde pequenos grupos polares podem formar-se em
coindições de zero-field-cooling (ZFC). Estes nanodomínios são considerados
como os núcleos do estado de polarização oposta e podem ser responsáveis
pelo menor campo coercitivo para este corte de cristal em particular. No
entanto, a histerese local piezoelétrica realizada pelo PFM à escala
nanométrica indica uma mudança de comportamento de PZN-PT semelhante
para ambas as orientações cristalográficas investigadas. A evolução das
estruturas de domínio com polimento abaixo da superfície do cristal foi
investigada. O domínio de ramificações e os efeitos de polarização de triagem
após o polimento e as medições de temperatura têm sido estudados pela PFM
e pela análise SEM. Além disso, verificou-se que a intensidade do sinal
piezoeléctrico a partir das estruturas de nanodomínio diminui com o aumento
da temperatura, acabando por desaparecer aos 430 K (orientaçáo ) e
470 K (orientação ). Esta diferença de temperatura nas transições de
fase local em cristais de diferentes orientações é explicada pelo forte efeito de
superfície na transição da fase ferroelétrica em relaxors.A comutação da polarização em relaxor ergódico e nas fases ferroeléctricas do
sistema PMN-PT foram realizadas pela combinação de três métodos,
Microscopia de Força Piezoeléctrica, medição de um único ponto de
relaxamento eletromecânico e por ultimo mapeamento de espectroscopia de
tensão. A dependência do comportamento do relaxamento na amplitude e
tempo da tensão de pulso foi encontrada para seguir um comportamento
logarítmico universal com uma inclinação quase constante. Este
comportamento é indicativo da progressiva população dos estados de
relaxamento lento, ao contrário de uma relaxação linear na presença de uma
ampla distribuição do tempo de relaxamento. O papel do comportamento de
relaxamento, da não-linearidade ferroeléctrica e da heterogeneidade espacial
do campo na ponta da sonda de AFM sobre o comportamento do ciclo de
histerese é analisada em detalhe. Os ciclos de histerese para ergódica PMN-
10%PT são mostrados como cineticamente limitados, enquanto que no PMN,
com maior teor de PT, são observados verdadeiros ciclos de histerese
ferroeléctrica com viés de baixa nucleação.In this thesis, Pb-based relaxor ferroelectrics of the (Pb,La)(Zr,Ti)O3 (PLZT),
Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT), Pb(Zn1/3,Nb2/3)O3-PbTiO3 (PZN-PT)
families were investigated and analyzed. Ferroelectric and dielectric properties
of the samples were studied by conventional macroscopic methods and locally
by piezoresponse force microscopy (PFM).
In PLZT 9.75/65/35 ceramics the nanoscale PFM contrast was investigated as
a function of grain size and grain orientation. It was found that the intensity of
piezoresponse signal from nanodomain structure decreases with temperature
and it disappears at 490 K (La mol. 8%) and 420 K (9.5%). Local hysteresis
loops were obtained as a function of temperature. The evolution of the
macroscopic and local parameters with temperature suggests strong surface
effect on ferroelectric phase transition in the investigated materials. The domain
wall roughness is determined with PFM for the natural domain structure
existing in this polycrystalline ferroelectric. Besides, artificial ferroelectric
domains were created by application of voltage pulses to the conducting PFM
tip, and the in-plane domain size was measured as a function of pulse duration.
All these experiments result in the conclusion that the domain wall in PZT-type
relaxors is quasi one-dimensional interface. The mechanism of the surface
contrast in PLZT-type relaxors is uncovered by PFM.
Domain structures vs. depth evolution was studied in PZN-4.5%PT crystals
with different orientation via PFM. Irregular domain patterns with the typical
sizes 20-100 nm were observed on the (001)-oriented surfaces of unpoled
samples. On the contrary, (111) crystal cuts exhibit normal micron-size regular
domains with the domain boundaries directed along allowed crystallographic
planes. The existence of nanodomains in (001)-oriented crystals is tentatively
attributed to the relaxor nature of PZN-PT where small polar clusters may form
under zero-field-cooling (ZFC) conditions. These nanodomains are considered
as the nuclei of the opposite polarization state and can be responsible for the
smaller coercive field for this particular crystal cut. However, local piezoelectric
hysteresis performed by PFM on the nanometer scale indicates similar
switching behavior of PZN-PT for both investigated crystallographic
orientations. Evolution of the domain structures with polishing below the crystal
surface has been investigated. The domain branching and polarization
screening effects after polishing and temperatures measurements have been
studied by PFM and SEM analysis. In addition, it was found what the intensity
of piezoresponse signal from nanodomain structures decreases with
temperature and finally disappears at 430 K ( orientation) and 470 K
( orientation). This difference of the temperature of local phase
transitions for crystals of different orientaions is explained by strong surface
effect on ferroelectric phase transition in relaxors.
Polarization switching in ergodic relaxor and ferroelectric phases in the PMNPT
system is studied using Piezoresponse Force Microscopy, single point
electromechanical relaxation measurements, and voltage spectroscopy
mapping. The dependence of relaxation behavior on voltage pulse amplitude
and time was found to follow a universal logarithmic behavior with a nearly
constant slope. This behavior is indicative of the progressive population of
slow relaxation states, as opposed to a linear relaxation in the presence of a
broad relaxation time distribution. The role of relaxation behavior,
ferroelectric non-linearity, and the spatial inhomogeneity of the tip field on
hysteresis loop behavior is analyzed in detail. The hysteresis loops for
ergodic PMN-10%PT are shown to be kinetically limited, while in PMN with
larger PT content, true ferroelectric hysteresis loops with low nucleation
biases are observed.FCT - SFRH/BD/22391/200
