A. K. Bandyopadhyay

Phonon dynamics of Zn"Mg,Cd…O alloy nanostructures and their phase segregation

In this paper we report phonon dynamics in chemically synthesized Zn 1�x Mg x O 0x 0.07 and Zn1�yCdyO 0y 0.03 alloy nanostructures of sizes 10 nm using nonresonant Raman and Fourier transformed infrared spectroscopy. Substitution by Mg makes the unit cell compact while Cd substitution leads to unit cell expansion. On alloying, both A1 LO and E1 LO mode of wurtzite ZnO show blueshift for Zn1�xMgxO and redshift for Zn1�yCdyO alloy nanostructures due to mass defect and volume change induced by the impurity atoms. Significant shift has been observed in E 1 LO mode for Zn 1�x Mg x O 73 cm �1 for x = 0.07 and Zn 1�y Cd y O 17 cm �1 for y = 0.03 nanostructures. The variation in ZnMg,Cd–O bond length determined from the blue- red- shift of IR bands on alloying with Mg Cd is consistent with their respective ionic sizes and the structural changes predicted by x-ray diffraction study. However, on progressive alloying one can detect phase segregation due to presence of interstitial Mg and Cd ions in the alloy nanostructures for relatively higher Mg and Cd concentrations. This is confirmed by the gradual absence of the characteristic IR and Raman bands of wurtzite ZnO near 400– 600 cm �1 as well as by x-ray and TEM studies.

Final Report on Key Comparison CCM.P-K7 in the range 10 MPa to 100 MPa of hydraulic gauge pressure

This report describes a CCM key comparison of hydraulic pressure standards of nine National Metrology Institutes that was carried out in the period from November 2002 to June 2004 in order to determine their degrees of equivalence in the range 10 MPa to 100 MPa of the gauge pressure. The pilot laboratory was PTB. The primary pressure standards were pressure balances of different design equipped with piston-cylinder assemblies operated in freedeformation, controlled-clearance or re-entrant operation mode. The transfer standard was a pressure balance equipped with a piston-cylinder assembly and a mass set. The pressuredependent effective areas of the transfer standard at specified pressures were reported by the participants and led to the reference values calculated as medians. All participants’ results agree with the reference values and with each other within the expanded uncertainties calculated with a coverage factor 2, most of them even within their standard uncertainties. In addition, the results were analysed in terms of the zero pressure effective area and the pressure distortion coefficient. Also for them agreement within expanded uncertainties (k=2) is observed. The results of the comparison demonstrate equivalence of the laboratory standards and support their measurement capability statements.

Cubic to hexagonal structural transformation in Gd2O3 at high pressure

High-pressure X-ray diffraction studies on gadolinium sesquioxide (Gd2O3) have been carried out up to a pressure of ∼25 GPa in a diamond-anvil cell at room temperature. Gadolinium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase at around 12 GPa. The high-pressure phase has been identified as a hexagonal La2O3-type structure. The bulk modulus and its pressure derivative of this phase have been calculated.

Band structure calculation and structural stability of high pressure phases of EuSe

Ab-initio band structure calculations have been carried out to find the pressure-induced structural transitions and structural stability of the magnetic semiconductor EuSe. The first principal tight-binding linear muffin-tin orbital method (TB-LMTO) within local density approximation (LDA) has been used to study this band structure. While the magnetic phase stability is determined from the total energy calculations within the atomic-sphere approximation (ASA) for both the non-magnetic (NM) and magnetic (M) phases. Our pure theoretical calculations show that: (1) at ambient pressure, the M phase is more stable than the NM phase; and (2) it exhibits a phase transition from NaCl (B1) type to CsCl (B2) type structure at around 9.48 GPa. Although the calculated lattice parameter, transition pressure, volume of collapse is found to be less than the experimentally observed value, but this has been explained from the fact that the calculation has been carried out at 0 K while the experiments have been performed at room temperature. The bulk modulus and magnetic moments are found to be in agreement with earlier experimental result.

The effect of pressure-transmitting fluids in the characterization of a controlled clearance piston gauge up to 1 GPa

The present paper describes the effect of different pressure-transmitting fluids (PTFs) on the systematic characterization of an oil-operated controlled clearance piston gauge (nominal diameter of the piston, 2.5?mm) in the pressure range up to 1000?MPa (1?GPa). Pure PTFs and mixtures of different PTFs are studied and four of them will be discussed here: namely (a) pure normal hydraulic oil (J-13), (b) a mixture of J-13 and an aviation turbine fuel (ATF), (JATF), (c) a pure di-ethyl-hexyl-sebacate oil (BIS) and (d) a mixture of white gasoline (G), J-13 and sebacate (GJBIS).The characterization is the measurement of the fall-rate of the piston as a function of applied jacket pressure (pj) with various PTFs using the method of Heydemann and Welch (HW model) (Heydemann and Welch 1975 Experimental Thermodynamics vol II, ed B Leneindre and B Voder (London: Butterworths) p 147). The analysis of the results is the determination of the cube root of the piston fall-rate (v1/3) with pj at different loads or measured pressures (pm). The linear portion of this v1/3?pj curve is extrapolated towards the null value of fall-rate, and the stall jacket pressure (pz) at different pm is obtained. It is observed that reasonably good fall-rate data could be obtained for J-13, JATF and BIS up to maximum pressures of 500?MPa, 700?MPa and 650?MPa, respectively. For GJBIS, these fall-rate data can be obtained up to a maximum pressure of 1?GPa. From the values of pz at different pm and also the values of the jacket pressure coefficient (d) along with other characteristic parameters in the HW model (Newhall et al 1979 Rev. Sci. Instrum. 50 964?8, Bandyopadhyay and Olson 2006 Metrologia 43 573?82), we have determined the relative standard uncertainties in the effective area (u(Ae)/Ae) for GJBIS up to 1?GPa for pj = 0 (free deformation mode) and pj/pm = 0.3. It is interesting to note that for pj = 0, at a pm of 100?MPa, u(Ae)/Ae is 74 ? 10?6, while at a pm of 1?GPa, u(Ae)/Ae is 248 ? 10?6. However, for pj/pm = 0.3, at a pm of 100?MPa, u(Ae)/Ae is 67 ? 10?6, while at a pm of 1?GPa, u(Ae)/Ae is 125 ? 10?6. A comparative study of u(Ae)/Ae has been elaborated with the four PTFs investigated. We have shown that at a pm of 100?MPa, u(Ae)/Ae is 202 ? 10?6, 114 ? 10?6, 66 ? 10?6 and 67 ? 10?6, for J-13, JATF, BIS and GJBIS, respectively, while at a pm of 500?MPa, u(Ae)/Ae is seen to be 97 ? 10?6, 57 ? 10?6, 46 ? 10?6 and 56 ? 10?6 for J13, JATF, BIS and GJBIS, respectively. Our measurements show that GJBIS is a convenient PTF for working up to 1?GPa. Finally, the results of the characterization are compared with the NPLI pressure scale through calibration of a NPLI secondary standard which is traceable to the LNE (France) pressure scale though direct comparison and participation in a recently concluded bilateral comparison with NIST (USA).

Intercomparison of National Hydraulic Pressure Standards up to 500 MPa

In order to provide inputs for improving the quality of measurements, achieving objective evidences of the technical competence and to build-up and maintain mutual confidence of national hydraulic pressure standards, an extensive in-house laboratory intercomparison is carried out in a systematic manner. The present paper describes the summary of the results thus obtained in this in-house laboratory intercomparison exercise of eight numbers of national hydraulic pressure standards, designated as NPL28MPA, NPL100MPN, NPL100MPA, NPL140MPA, NPL200MPN, NPL280MPA, NPL500MPN, NPL500MPA. The intercomparison of these pressure standards is carried out using an internationally accepted method of cross-floating of pressure balances. The uncertainty in area and pressure measurements is computed as per ISO, WECC and EAL guidelines. The compatibility, uniformity and affirmation of results is re-established by comparing the values of zero pressure effective area (A 0) and distortion coefficient (Λ) with the values obtained during bilateral and international key comparisons sponsored by BIPM, CCM, APLAC, LNE (France) and NIST (USA). The metrological characteristics thus obtained establish a very good agreement within the limits of uncertainty budgets of bilateral and international key comparisons.

Phase transition in a perovskite superconductor by radiation-induced lattice excitations

We report (2212) → (2223) phase modification in a mixed phase, Bi-based oxide superconductor. In contrast to established procedures, this has been possible employing high-energy ion irradiation at 80 K. A nucleation process, assisted through radiation-induced vacancy creation and their subsequent annihilation by the existing interstitials, is shown to achieve the observed phase transformation.

Anharmonic behavior and structural phase transition in Yb2O3

The investigation of structural phase transition and anharmonic behavior of Yb2O3 has been carried out by high-pressure and temperature dependent Raman scattering studies respectively. In situ Raman studies under high pressure were carried out in a diamond anvil cell at room temperature which indicate a structural transition from cubic to hexagonal phase at and above 20.6 GPa. In the decompression cycle, Yb2O3 retained its high pressure phase. We have observed a Stark line in the Raman spectra at 337.5 cm−1 which arises from the electronic transition between 2 F 5/2 and 2 F 7/2 multiplates of Yb3+ (4f 13) levels. These were followed by temperature dependent Raman studies in the range of 80–440 K, which show an unusual mode hardening with increasing temperature. The hardening of the most dominant mode (T g + A g ) was analyzed in light of the theory of anharmonic phonon-phonon interaction and thermal expansion of the lattice. Using the mode Gruneisen parameter obtained from high pressure Raman measurements; we have calculated total anharmonicity of the T g + A g mode from the temperature dependent Raman data.

High pressure behavior of nano-crystalline CeO2 up to 35 GPa: a Raman investigation

The present paper reports the results of in situ Raman studies carried out on nano-crystalline CeO2 up to a pressure of 35 GPa at room temperature. The material was characterized at ambient conditions using X-ray diffraction and Raman spectroscopy and was found to have a cubic structure. We observed the Raman peak at ambient at 465 cm−1, which is characteristic of the cubic structure of the material. The sample was pressurized using a diamond anvil cell using ruby fluorescence as the pressure monitor, and the phase evolution was tracked by Raman spectroscopy. With an increase in the applied pressure, the cubic band was seen to steadily shift to higher wavenumbers. However, we observed the appearance of a number of new peaks around a pressure of about 34.7 GPa. CeO2 was found to undergo a phase transition to an orthorhombic α -PbCl2-type structure at this pressure. With the release of the applied pressure, the observed peaks steadily shift to lower wavenumbers. On decompression, the high pressure phase existed down to a total release of pressure.

Temperature dependent variations of phonon interactions in nanocrystalline cerium oxide

The temperature dependent anharmonic behavior of the phonon modes of nanocrystalline CeO2 was investigated in the temperature range of 80-440 K. The anharmonic constants have been derived from the shift in phonon modes fitted to account for the anharmonic contributions as well as the thermal expansion contribution using the high pressure parameters derived from our own high pressure experimental data reported previously. The total anharmonicity has also been estimated from the true anharmonicity as well as quasiharmonic component. In the line-width variation analysis, the cubic anharmonic term was found to dominate the quartic term. Finally, the phonon lifetime also reflected the trend so observed.