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Title: Anomalous elastic behavior of polycrystalline Nb 2O 5

Abstract

The Young's modulus of polycrystalline niobium pentoxide was investigated as a function of temperature using the sonic resonance technique.

Authors:
 [1]
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  1. Iowa State Univ., Ames, IA (United States)
Publication Date:
Research Org.:
Ames Lab., Ames, IA (United States)
Sponsoring Org.:
US Atomic Energy Commission (AEC)
OSTI Identifier:
4015260
Report Number(s):
IS-T-446
NSA Number:
NSA-25-042955
DOE Contract Number:
W-7405-ENG-82
Resource Type:
Thesis/Dissertation
Resource Relation:
Other Information: Thesis. UNCL. Orig. Receipt Date: 31-DEC-71
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ELASTICITY; FABRICATION; HOT PRESSING; NIOBIUM OXIDES; POLYCRYSTALS; SINTERING; TEMPERATURE; YOUNG MODULUS; NIOBIUM OXYBROMIDES/elastic properties of polycrystalline Nb$sub 2$O$sub 5$, effects of fabrication methods and temperature on

Citation Formats

Manning, William Roger. Anomalous elastic behavior of polycrystalline Nb2O5. United States: N. p., 1971. Web. doi:10.2172/4015260.
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Manning, William Roger. Anomalous elastic behavior of polycrystalline Nb2O5. United States. doi:10.2172/4015260.
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Manning, William Roger. Tue . "Anomalous elastic behavior of polycrystalline Nb2O5". United States. doi:10.2172/4015260. https://www.osti.gov/servlets/purl/4015260.
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@article{osti_4015260,
title = {Anomalous elastic behavior of polycrystalline Nb2O5},
author = {Manning, William Roger},
abstractNote = {The Young's modulus of polycrystalline niobium pentoxide was investigated as a function of temperature using the sonic resonance technique.},
doi = {10.2172/4015260},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Jun 01 00:00:00 EDT 1971},
month = {Tue Jun 01 00:00:00 EDT 1971}
}
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Thesis/Dissertation:
View Thesis/Dissertation (6.35 MB)
DOI:  10.2172/4015260
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  • The electrical conductivity of alpha -Nb/sub 2/O/sub 5/ and Nb/sub 2/O/ sub 4/ wa s measured by means of a standard four probe d-c technique as a function of both the composition over the entire range of homogeneity of the oxide phases and the temperature over the range 77 to 1273 un. Concent 85% K. The measurements were made on pressed and sintered specimens of known and constant composition. The conductivity data for both alpha -Nb/sub 2/O/sub 5/ and Nb/sub 2/O/sub 4/, along with literature values for NbO, are interpreted in terms of the standard band model proposed by Morinmore » for the 3d transition metal oxides and used here for the 4d transition metal oxides. The 4d band of the Nb ions forms the conduction band, while the 2p band of the O ions forms the valence band. The forbidden energy gap between these two bands appears to be 4 ev wide. Located within thia forbidden gap is a donor level (indicated by the sign of the thermoelectric power), which arises from the metal-excess defect. This defect may be either singly ionizable O ion vacancies or triply or quadruply ionizable interstitial Nb ions. In the fixed-composition data for heavily reduced gamma Nb/sub 2/O/sub 5/, an exhaustion region at high temperatures permits the calculation of an absolute value for the mobility of electrons in the 4d conduction band to be made. The magnitude of the mobility is 0.4 cm/sup 2//v sec and follows a T/sup -0.5/ law. At lower temperatures, a thermally activated process is observed which is attributed to the excitation of electrons from the metal-excess defect. The excitation energy for the defect decreases as the concentration of defects increases according to the Meyer-Neldel rule. The values range from 0.3 to 0.003 ev. The outstanding characteristic of the Nb/sub 2/O/sub 4/ data is the transformation temperature at 1070 un. Concent 85% K, which is believed to be a magnetic interaction due to a collapsing of a split 4d band. The conductivity in Nb/sub 2/O/sub 4/, an n-type semiconductor, is independent of composition in the very narrow range of homogeneity. A close similarity of the electrical properties of the Nb oxides to those of the Ti oxides is observed, indicating that the same type of mechanism of conduction is probably occurring in both oxide systems. (Dissertation Abstr.)« less

  • Elastic properties and internal friction of selected compositions of tantala-doped monoclinic europia were studied at temperatures up to 1500°C using the sonic resonance technique. Unit cell parameters between 25C and 1000°C for monoclinic Eu 2O 3 were calculated from high temperature x-ray diffractometer data. Large-grained monoclinic specimens having less than 6.0 Ta cation percent substitution exhibited anomalous elastic behavior when thermally cycled. Compositions above this addition level exhibited linear elastic behavior. Internal friction values also varied abnormally with grain size, composition, and temperature. The anomalous behavior was attributed to microcracking caused by thermal expansion anisotropies. The critical grain size wasmore » found to be approximately 14 μm. The high temperature diffractometry measurements supported the postulate that the grain coarsening effect associated with sintered monoclinic Eu 2O 3 is the controlling factor for microcracking.« less

  • A resonant frequency technique was used to determine the effect that temperature and porosity have been on the elastic properties of gadolinia, while the temperature dependence of thermal diffusivity was investigated by a flash method.

  • Thesis. The method of chemical transport reaction was particularly suitable for the production of Nb/sub 2/,O/sub 5/ single crystals. The crystal structure of a new Nb/sub 2/O/sub 5/ modification was determined with the heavy- atom method. An additional new modiflcation could not be obtained as a pure single crystal, but the principles of the structure could be established. For octahedral structures, a system was developed in such a way that the properties of related transition metal oxides could be predicted. (11 tables, 22 figures, 98 references) (HBG)