High-resolution synchrotron XRD study of Zr-rich compositions of Pb(Zr_xTi_1-x)O_3 (0.525\leq x \leq 0.60): evidence for the absence of the rhombohedral phase

Results of Rietveld analysis of the synchrotron XRD data on Pb(Zr_xTi_1-x)O_3 (PZT) for 0.525\leqx\leq0.60 are presented to show the absence of rhombohedral phase on the Zr-rich side of the morphotropic phase boundary (MPB). Our results reveal that the structure of PZT is monoclinic in the Cm space group for 0.525\leq x\leq 0.60. The nature of the monoclinic distortion changes from pseudo-tetragonal for 0.525\leqx\leq0.54 to pseudo-rhombohedral for x>0.54.Comment: 12 pages, 5 figur

The Relationship Between Well-Structured And Ill-Structured Problem Solving In Multimedia Simulation

Problem solving, especially complicated ill-structured problem solving, has been a major concern in education. Research of the past decade provides qualitative ways of viewing the solving processes of ill-structured problems. Sinnott, Voss & Post, and Jonassen suggested that ill-structured problem solving has to support new, more qualitative, components than those for solving well-structured problems. This study set forth to test the theory that the problem-solving skills used for wellstructured problems are necessary but not sufficient for solving ill-structured problems in the context of an open-ended, multimedia problem-solving environment Two sets of open-ended questions were posed to reflect students’ solving skills in well-structured and ill-structured problems involving astronomy contexts. Additionally, various instruments including domain-specific knowledge, structural knowledge, and justification skills were developed to measure students’ necessary cognitive components for solving problems. Finally, inventories such as science attitude, motivation in astronomy, knowledge of cognition, and regulation of cognition were employed to collect the appropriate data of metacognition and non-cognitive variables. Generalized, judgmental scoring systems were developed using a quantitative index intended to reflect the extent to which subjects possessed solving skills as well as certain cognitive components of well-structured and ill-structured problems. The results of this study verified past research conclusions that well-structured and ill-structured problems require different necessary components for reaching successful solutions. In overall, cognition, including domain-specific knowledge and structural knowledge, and justification skills were critical components for successful solution in wellstructured problem solving. Alternatively, metacognition, non-cognitive variables, justification skills, as well as cognition, were found to be essential components needed to solve ill-structured problems. Implications for science education in a multimedia simulation environment, assessment on problem solving, and problem-solving research are presented

Results of a Survey Assessing the Impact of Astronomy Village: Investigating the Universe

Abstract This paper discusses the results of a follow-up questionnaire administered to over 300 registered owners of Astronomy Village ® : Investigating the Universe™. The results indicate that teachers who used the software were very pleased with it. They felt that students were learning a variety of science related skills. It was also determined that the greatest barriers teachers face in adopting Astronomy Village are lack of proper equipment and lack of time

The covalent bonding interaction in the ferroelectric LuMnO(3)

The electron density distributions of paraelectric and ferroelectric LuMnO3 are analyzed using high temperature synchrotron x-ray powder diffraction data with the Rietveld method, the maximum entropy method (MEM), and MEM-based pattern fitting. Bonding electrons due to orbital hybridization are clearly seen in the Lu1-O3 and Lu2-O4 bonds along the c-axis polarization direction. The Lu1-O3 bond was determined to be covalent due to hybridization below the ferroelectric transition temperature, and was identified as the driving force for ferroelectricity in LuMnO3. However, the Lu2-O4 bond shows covalent character in both paraelectric and ferroelectric states. Also, we suggest that the Lu2-O4 covalent bonding is responsible for large spontaneous polarization in LuMnO3, associated with the small radius of the Lu3+ ion. (C) 2011 American Institute of Physics. [doi:10.1063/1.3655986]open1155sciescopu

A study of phase coexistence and temperature dependent monoclinic to tetragonal phase transition in the multiferroic (1-x)Pb(Fe<SUB>1/2</SUB>Nb<SUB>1/2</SUB>)O<SUB>3</SUB>-xPbTiO<SUB>3</SUB> (x=0.08)

The origin of coexistence of tetragonal and monoclinic phases in the morphotropic phase boundary (MPB) region of (1-x)Pb(Fe1/2Nb1/2)O3-xPbTiO3 has been investigated for x=0.08 by synchrotron x-ray powder diffraction in the 10-550 K range. It is shown that the phase coexistence observed at room temperature in the MPB region is essentially due to a first order phase transition between the low temperature monoclinic and high temperature tetragonal phases. This transition is shown to be accompanied with a phase coexistence over a very wide temperature range (&#916;T~200 K) across the room temperature

Nanorod-assembled spinel Li1 05Mn1 O-95(4) rods with a central tunnel along the rod-axis for high rate capability of rechargeable lithium-ion batteries

Nanorod-assembled spinel Li1 05Mn1 95O4 rods with a central tunnel along the rod-axis were synthesized using highly crystalline beta-MnO2 rods as self-templates The synthesized spinel Li1 05Mn1 95O4 is an assembly of several single crystal-like nanorods with an average diameter and length of 100 and 400 nm respectively which was determined by microstructural Rietveld refinement using the synchrotron powder XRD data Galvanostatic battery testing showed that central-tunneled and nanorod-assembled Li1 05Mn1 95O4 rods have a high charge storage capacity at high current densities in comparison with those of the simnel rods without a tunnel structure and commercial powders Moreover a capacity retention value of 81% was observed at the end of 100 cycles at a current of 250 mAh g(-1

Evidence for monoclinic crystal structure and negative thermal expansion below magnetic transition temperature in Pb(Fe<SUB>1/2</SUB>Nb<SUB>1/2</SUB>)O<SUB>3</SUB>

The existing controversy about the room temperature structure of multiferroic Pb(Fe1/2Nb1/2)O3 is settled using synchrotron powder x-ray diffraction data. Results of Rietveld refinements in the temperature range of 300-12 K reveal that the structure remains monoclinic in the Cm space group down to 12 K, but the lattice parameters show anomalies at the magnetic transition temperature (TN) due to spin-lattice coupling. The lattice volume exhibits negative thermal expansion behavior, with a=-4.64&#215;10-6K-1, below TN