Microstructure characterization of high-pressure induced texture in fully densified zirconium diboride ceramics

Fully dense oriented monolithic zirconium diboride (ZrB₂) ceramics with <0001> fiber texture were fabricated using high-pressure spark plasma sintering. The <0001> fiber texture is proposed to be triggered by grain rotation, as (0001) <$11\overline{2}0$> basal $⟨a⟩$ slip of ZrB₂ was activated during sintering. The high temperature, uniaxial high pressure, and uniform starting particles play a vital role in the texture formation of ZrB₂ ceramics. The result provides visible evidence for the occurrence of plastic deformation during high-pressure-assisted sintering.     

A Portmanteau Test for Smooth Transition Autoregressive Models

This article investigates a portmanteau test statistic for checking model adequacy of smooth transition autoregressive (STAR) models. The asymptotic distribution of residual autocorrelations and the least-squares estimators are also derived. Hence, the correct asymptotic standard errors for residual autocorrelations are also obtained facilitating model diagnostic checking. Through the graphical display of the simulation results concerning the size and power, for commonly used nominal sizes ($\le 0.1$), the portmanteau test appears to be more advantageous than the Lagrange multiplier tests in checking serial independence for the errors of STAR models.     

Phase pure rhombohedral R3¯m$R\bar{3}m$ AgCoO2 delafossite: Rietveld,selected area electron diffraction,X-ray photoemission spectroscopy,and magnetic studies

A p-type rhombohedral AgCoO₂ (S.G. $R\overline{3}m$) reported to form only at pressures greater than 300 MPa at 773 K, is stabilized in pure phase at 0.2 MPa oxygen pressure. Analysis of powder X-ray diffraction pattern by Rietveld and selected area electron diffraction patterns confirms the purity of rhombohedral phase. Core-shell X-ray photoemission spectroscopy studies show that Ag ions are in +1 oxidation state with Co ions largely in +3 state. AgCoO₂ is paramagnetic undergoing super-paramagnetic transition at 44 K. The magnetic moment of Co is 0.001 μB which corresponds to low spin (LS) Co³⁺ along with a small fraction of LS Co⁴⁺ ions.