The morphotropic phase boundary in the phase diagram of the technologically important Pb(Zr x Ti 1Àx )O 3 (PZT) ceramics has been traditionally believed to separate ferroelectric tetragonal and rhombohedral phase regions. This old picture has come under close scrutiny during the last eight years following the discovery of new monoclinic phases in the Cm and Cc space groups. This article presents a brief overview of these discoveries in which the use of multiple diffraction probes (X-ray, electron, neutron diffraction) in conjunction with physical property measurements has played a crucial role. A new phase diagram of PZT showing the stability fields of these structures below room temperature is also presented.

The Er3+/Yb3+/Bi3+ tri-doped La2O3 nano-phosphor gives efficient induced optical heating and temperature sensing. This study is useful to understand these characteristics in different materials with various pump powers and temperatures.

A negative-positive-negative switching behavior of magnetoresistance ͑MR͒ with temperature is observed in a ferromagnetic shape memory alloy Ni 1.75 Mn 1.25 Ga. In the austenitic phase between 300 and 120 K, MR is negative due to s-d scattering. Curiously, below 120 K MR is positive, while at still lower temperatures in the martensitic phase, MR is negative again. The positive MR cannot be explained by Lorentz contribution and is related to a magnetic transition. Evidence for this is obtained from ab initio density-functional theory, a decrease in magnetization and resistivity upturn at 120 K. Theory shows that a ferrimagnetic state with antiferromagnetic alignment between the local magnetic moments of the Mn atoms is the energetically favored ground state. In the martensitic phase, there are two competing factors that govern the MR behavior: a dominant negative trend up to the saturation field due to the decrease in electron scattering at twin and domain boundaries and a weaker positive trend due to the ferrimagnetic nature of the magnetic state. MR exhibits a hysteresis between heating and cooling that is related to the first-order nature of the martensitic phase transition.

The structure of orthorhombic (α″) martensitic phase of Ti–8Nb, Ti–12Nb, and Ti–16Nb alloys has been investigated using Rietveld refinement of x-ray diffraction data. The chemical analysis data have been used to determine the site occupancy of initial models. A limit of the Wyckoff positions has been proposed based on the symmetry of the Cmcm space group, which allows the movement of atoms without breaking the space group symmetry. This has also been incorporated in the initial models of experimental alloys, and accordingly Wyckoff positions have been refined. It has been observed that the atoms move along the Y-axis (parallel to the b-axis) and the movement of atoms increases with increase in Nb concentration. The formation of orthorhombic (α″) phase has been explained based on the movement of atoms along the Y-axis. This in turn breaks the hexagonal symmetry and forms an orthorhombic phase.

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