Origin of the Giant Piezoelectric Properties in the [001] Domain Engineered Relaxor Single Crystals

International audienceRelaxor single crystals PZN-9%PT have been cut and poled along [1̄01] direction for which the spontaneous polarization Ps is approximately parallel to the poling field Ep. The piezoelectric matrix of the monoclinic single-domain (1M state) has been determined, in the approximation of an orthorhombic symmetry. The shear mode (15) along [101], gives the highest electromechanical coupling factor k15 (andgt;80%) and the largest piezoelectric coefficient d15 (∼3200 pC/N). The properties of the disoriented 1M state have been calculated from a change of axes. The maximum of d33θphi; is obtained along a direction close to [001]. This is due to the very large value of d15 compared to d30 in the basic 1M state. On the other hand the transverse piezoelectric coefficient along [uv0] for the [001] disoriented Ps single domain presents a strong anisotropy. Finally, in the [001] domain engineered configuration, an important extrinsic contribution of the domain coexistence is evidenced by comparing calculated and measured coefficients

Correlation of radiation-induced changes in microstructure/microchemistry, density and thermo-electric power of type 304L and 316 stainless steels irradiated in the Phénix reactor

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Electric-field-induced orthorhombic phase in Pb[(Zn1/3Nb2/3)(0.955)Ti-0.045]O-3 single crystals

International audienceThe ferroelectric phase transitions of [(1) over bar 01]-, [001]-, and [111]-oriented Pb[Zn1/3Nb2/3]O-3-4.5%PbTiO3 (PZN-4.5%PT) single crystals were investigated as a function of temperature (T between 300 and 450 K), and electric field (E field between 0 and 300 kV/m) by dielectric and x-ray diffraction combined measurements. Under null E field, PZN-4.5%PT exhibits the following phase transitions: cubic (C)-->tetragonal (T)-->rhombohedral (R), during cooling. Under E field applied on a [(1) over bar 01]-oriented single crystal, an intermediate orthorhombic (O) ferroelectric phase is induced at temperatures intermediate between that of the T and R phases. The temperature range of existence of this O phase depends both on the crystal orientation and on the measurement conditions: field cooling (FC), zero-field heating after field cooling (ZFHAFC), or field heating (FH). When E field is applied along [(1) over bar 01], the stability range is within 40 K in FC and only 15 K in ZFHAFC; when E field is applied along [001] or [111], this range is still narrower. The O phase is not even observed in FH for [001] orientation and in FC for [111] orientation. These observations show that the application of an E field favors the transition to an O phase, leading to a single-domain structure, when the direction of the field is parallel to the spontaneous polarization [(1) over bar 01] directio

Microstructural evolutions and cyclic softening of 9%Cr martensitic steels

International audienceDetailed TEM and EBSD measurements were carried out to quantify the microstructural evolutions and to identify the physical mechanisms taking place during fatigue and creep-fatigue at 823 K on a P91 martensitic steel. The coarsening of former martensitic laths is shown to be heterogeneous for low applied strains, whereas for higher applied strains and longer holding periods the whole microstructure coarsens. Based on these observations and on a careful study of the stress partition (backstress, isotropic and viscous stress), the softening effect in creep-fatigue is found to be mainly related to the cumulated viscoplastic strain at a given fatigue strain range. The microstructural coarsening taking place during cyclic loadings is shown to increase significantly the minimum creep rate of this steel

Domain structures in monoclinic Pb[(Zn1/3Nb2/3)0.91Ti0.09] O3 poled single crystals

International audienceA tetragonal (T) ↔ monoclinic (M) phase transition characterized by a wide thermal hysteresis is observed in Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) single crystals close to the morphotropic composition PZN-9%PT. The domain structure of crystals, determined by X-ray diffraction and optical observations, is dependent on the poling crystallographic direction. A monoclinic quasi-single domain structure is obtained by poling along the pseudocubic [101] direction whereas an unexpected monoclinic multidomain state with macroscopic 2 mm symmetry can be obtained for [001] poled crystals. Finally it is shown that the largest piezoelectric response corresponds to the monoclinic multidomain state of [001] poled crystals

Domain engineering of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals and piezoelectric related properties

International audienceThe domain configuration and the electromechanical related properties have been studied in Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZN-9%PT) single crystals cut along [001] and [101̄]. It was established that soft (with high d) and hard (with lower d) piezoelectric properties are respectively obtained in a multidomain and a single domain configuration. The softer piezoelectric material (d33 - 2700 pC/N, S33 E = 180 pN/m2, k33 = 93%) was found in the monoclinic multidomain state after poling with a small field along [001]. Optimal poling process and electromechanical related properties of the single crystals were discussed in term of the field-temperature diagram

Microstructural characterizations of austenitic stainless steels representative of PWR internals irradiated with ions from low to high doses and comparison to cluster dynamic simulations

International audienceThe French nuclear industry is looking into the extension of the operation time of pressurized water reactors (PWR) up to 60 years. The lower parts of the internals are composed of Solution Annealed (SA) 304 austenitic stainless steel plates and Cold Worked (CW) 316 stainless steel bolts. Due to their high exposition to irradiation it is expected to reach doses as high as 120 dpa after 60 years, at temperatures in the range of 300 to 370°C. The microstructures under ion irradiations of two 304 austenitic stainless steels grades that mainly differ in carbon content are investigated by Transmission Electron Microscopy (TEM). The evolution of radiation-induced defects as cavities, Frank loops and precipitates with the dose are studied as well as the influence of carbon. Ion irradiations from 5 to 100 dpa have been carried out at JANNuS-Saclay facility on using iron ions (10 MeV). To counterbalance the flux effect, irradiation temperature was set to 450°C.As observed in PWR internals, Frank loop density and size reach saturation at about 5 dpa. This validates the chosen shift of temperature. Major precipitation is observed in both 304 at high doses, however precipitates appears earlier and in higher concentration in the higher carbon content steel. Voids are present, and are relatively small in size and in low density considering the dose. As the dose increases the mean size and void density increase as well, with exception at high doses in 304L where a bimodal size distribution is observed. Carbon and precipitation seem to delay germination of cavities. In-situ irradiation up to 1.5 dpa were also performed at JANNuS-Orsay facility. It allows to investigate the evolution and creation of defects in the early moment of irradiation. Apparition of black dots and evolution of the dislocation network (Frank loops and perfect dislocations) are visible at the very beginning of irradiation. Finally, the evolution of the microstructure under irradiation with time (doses) and space (along the damage profile) is successfully modelled using Cluster Dynamic (CD) code CRESCENDO. Calculations along the profile damage show that surface and injected interstitials have an effect on the microstructure and confirm experimental observations. The effect of the surface is observable on cavities and Frank loops, on a large depth. Also, injected interstitials have an effect on both cavities and Frank loops. Microstructures as a function of the depth are explained based on the coupling between experiments and CD calculation

Tensile properties and deformation microstructure of highly neutron-irradiated 316 stainless steels at low and fast strain rate

International audiencePost-irradiation deformation behavior of solution-annealed (SA) and cold-worked (CW) 316 austenitic stainless steel irradiated to doses from 9 to 39 dpa is examined as a function of strain rate and irradiation conditions (neutron spectrum, temperature). Tensile properties are found to be significantly higher for lower irradiation temperature and for CW material, for similar irradiation levels. The effect of strain rate on tensile properties is shown to be weak in the range [10−8s−1; 10−4s−1]. TEM investigations after deformation for levels of plastic strain of about 1percent show on SA 316 the presence of deformation bands corresponding to one or even a mixture of twins, extended stacking faults, alpha-martensite islands and ε-martensite nanobands. Bundles of crisscrossing bands, found to be a composite of overlapping stacking faults, nanotwins and ε-martensite nanolayers, are observed at TEM foils edges near the grain boundaries with α′-martensite islands decorating these edges. Except observation of a slight decrease of the number of deformation bands in the specimen deformed at slower strain rate, no qualitative microstructural differences appear between specimens tested at slow and fast strain rates

Evolution of microstructure after irradiation creep in several austenitic steels irradiated up to 120 dpa at 320°C

International audienceIrradiation creep was investigated in different austenitic steels. Pressurized tubes with stresses of 127–220 MPa were irradiated in BOR-60 at 320°C to 120 dpa. Creep behavior was dependent on both chemical composition and metallurgical state of steels. Different steels irradiated with and without stress were examined by TEM. Without stress, the irradiation produced high densities of dislocation lines and Frank loops and, depending on the type of steels, precipitates. Stress induced an increase of the precipitate mean size and density and, for some grades, an increase of the mean loop size and a decrease of their density. An anisotropy of Frank loop density or size induced by stress was not observed systematically. Dislocation line microstructure seems not to be different between the stressed and unstressed specimens. No cavities were detectable in these specimens. By comparing with the data from this work, the main irradiation creep models are discussed