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Crystallization
Published in George A. Lane, Solar Heat Storage: Latent Heat Materials, 1983
Geometric considerations reveal that there are only 14 basic types of crystal lattice. On the basis of symmetry these are grouped into seven crystal systems. Cubic or isometric — the three crystal axes are all equal and at right angles to one another.Tetragonal — two crystal axes are equal, the third unequal. All axes are at right angles.Orthorhombic — the three crystal axes are unequal. All axes are at right angles.Trigonal or rhombohedral — the three crystal axes are equal, two are at right angles and the third is not. This is now treated in the U.S. as a subsystem of the hexagonal crystal system.Monoclinic — the three axes are unequal. Two axes are at right angles, the third is not.Triclinic or anorthic — the three axes are unequal, and none is at right angles to another.Hexagonal — three coplanar, equal axes are at 60° to each other, the fourth axis is unequal and at right angles to the three.
Metamorphism
Published in Aurèle Parriaux, Geology, 2018
Research shows that one initial material can produce different minerals depending on environmental conditions. An excellent example is the aluminum silicate Al2siO5 (Fig. 11.9). Depending on the relative values of pressure and temperature, there are three different mineralogical forms: andalusite (orthorhombic), sillimanite (orthorhombic), and kyanite (triclinic). The presence of one of these minerals in a rock is used to determine three degrees of metamorphism, called “zones” (Fig. 11.10). Other zones can be defined on the basis of minerals that reflect environmental conditions.
Metamorphism
Published in Aurèle Parriaux, Geology, 2018
Research shows that one initial material can produce different minerals depending on environmental conditions. An excellent example is the aluminum silicate Al2SiO5 (Fig. 11.9). Depending on the relative values of pressure and temperature, there are three different mineralogical forms: andalusite (orthorhombic), sillimanite (orthorhombic) and kyanite (triclinic). The presence of one of these minerals in a rock is used to determine three degrees of metamorphism, called “zones” (Fig. 11.10). Other zones can be defined on the basis of minerals that reflect environmental conditions.
Impact of forsterite addition on mechanical and biological properties of composites
Published in Journal of Asian Ceramic Societies, 2020
Rajan Choudhary, Senthil Kumar Venkatraman, Inna Bulygina, Ankita Chatterjee, Jayanthi Abraham, Fedor Senatov, Sergey Kaloshkin, Artem Ilyasov, Maxim Abakumov, Marina Knyazeva, Dimitri Kukui, Frank Walther, Sasikumar Swamiappan
The XRD pattern (Figure 1(c)) of the diopside prepared by the sol-gel combustion method was matched and indexed as per standard JCPDS data card no. 900–1308. The crystal system of the diopside is monoclinic. The XRD pattern of forsterite (Figure 1(d)) was matched with the standard JCPDS card no. 900–0320 and indexed. The crystal system of forsterite was found to be orthorhombic.
Helicoidal ordering in NiMn1-xCrxGe for x = 0, 0.04, 0.11 and 0.18
Published in Phase Transitions, 2018
Bogusław Penc, Andreas Hoser, Stanisław Baran, Andrzej Szytuła
The polycrystalline samples were prepared by arc melting followed by annealing at 850 °C and finally slowly cooling down to room temperature. The preparation procedures are described in detail in Ref. [4]. The X-ray diffraction data at room temperature confirmed that the samples crystallized in the orthorhombic crystal structure.
Dielectric, impedance and modulus spectroscopy of Ta-based layered perovskite
Published in Phase Transitions, 2019
P. L. Deepti, S. K. Patri, R. N. P. Choudhary, P.S. Das
This paper summarizes the dielectric, conductivity and electrical properties of the ceramic sample PBT, which was prepared by using solid state reaction method, calcined at 1050°C and sintered at 1100°C. From the X-ray structural study, the crystal structure of the compound was found to be orthorhombic. The surface morphology studies show formation of grains over the entire surface of the sample having lenticular and plate shaped hybrid structure confirming highly anisotropic crystal structure of Aurivillius oxides. From the dielectric studies, it is clear that the material is normal ferroelectric in nature and it transforms from ferro to para at Tc around 478°C. With high-temperature evaluation, the nature of dielectric constant and loss of PBT makes it suitable for microwave and high power applications as high-temperature dielectrics materials. Further, its conduction mechanism was described by the hopping relaxation model. The activation energy on high-temperature zone is estimated to be 0.353 eV from the Arrhenius plot, which suggests a smaller energy is required for thermal excitation. The impedance behavior of PBT ceramics was investigated over a wide frequency and temperature range. From the impedance and modulus spectroscopic studies, the material showed relaxation effects which are non-Debye type. The relaxation frequencies shifted to a higher frequency side with an increase in temperature. Complex impedance spectroscopy permits us to endorse the grain (bulk) contributions in the materials. An equivalent circuit was used to demonstrate the electrical phenomena going on inside the materials. The grain resistance drops with a rise in temperature. Both Impedance and modulus analysis indicates the presence of grain contributions to the resistance in the material as we observe only one semicircular arc in both the complex spectrum plot. Both these analyses along with the conductivity studies also support the typical behavior of negative temperature coefficient of resistance of the materials. Finally, the non-linear characteristic curves justify the non-Ohmic nature of synthesized PBT sample.