PMID- 24295052
OWN - NLM
STAT- PubMed-not-MEDLINE
DCOM- 20140806
LR  - 20131227
IS  - 1520-5207 (Electronic)
IS  - 1520-5207 (Linking)
VI  - 117
IP  - 51
DP  - 2013 Dec 27
TI  - Ionic conductivity of mixed glass former 0.35Na(2)O + 0.65[xB(2)O(3) + (1 - 
      x)P(2)O(5)] glasses.
PG  - 16577-86
LID - 10.1021/jp409497z [doi]
AB  - The mixed glass former effect (MGFE) is defined as a nonlinear and nonadditive 
      change in the ionic conductivity with changing glass former fraction at constant 
      modifier composition between two binary glass forming compositions. In this 
      study, mixed glass former (MGF) sodium borophosphate glasses, 0.35Na2O + 
      0.65[xB2O3 + (1 - x)P2O5], 0 </= x </= 1, have been prepared, and their sodium ionic 
      conductivity has been studied. The ionic conductivity exhibits a strong, positive 
      MGFE that is caused by a corresponding strongly negative nonlinear, nonadditive 
      change in the conductivity activation energy with changing glass former content, 
      x. We describe a successful model of the MGFE in the conductivity activation 
      energy terms of the underlying short-range order (SRO) phosphate and borate glass 
      former structures present in these glasses. To do this, we have developed a 
      modified Anderson-Stuart (A-S) model to explain the decrease in the activation 
      energy in terms of the atomic level composition dependence (x) of the borate and 
      phosphate SRO structural groups, the Na(+) ion concentration, and the Na(+) 
      mobility. In our revision of the A-S model, we carefully improve the treatment of 
      the cation jump distance and incorporate an effective Madelung constant to 
      account for many body coulomb potential effects. Using our model, we are able to 
      accurately reproduce the composition dependence of the activation energy with a 
      single adjustable parameter, the effective Madelung constant, that changes 
      systematically with composition, x, and varies by no more than 10% from values 
      typical of oxide ceramics. Our model suggests that the decreasing columbic 
      binding energies that govern the concentration of the mobile cations are 
      sufficiently strong in these glasses to overcome the increasing volumetric strain 
      energies (mobility) caused by strongly increasing glass-transition temperatures 
      combined with strongly decreasing molar volumes of these glasses. The dependence 
      of the columbic binding energy term on the relative high-frequency dielectric 
      permittivity suggests that the increased polarizability of the bridging oxygens 
      connecting SRO tetrahedral boron units to phosphorus units causes further charge 
      delocalization away from the negatively charged tetrahedral boron units, leading 
      to a lowering of the charge density, and is the underlying cause of the MGFE.
FAU - Christensen, Randilynn
AU  - Christensen R
AD  - Department of Materials Science and Engineering Iowa State University , Ames, 
      Iowa 50011.
FAU - Olson, Garrett
AU  - Olson G
FAU - Martin, Steve W
AU  - Martin SW
LA  - eng
PT  - Journal Article
DEP - 20131212
PL  - United States
TA  - J Phys Chem B
JT  - The journal of physical chemistry. B
JID - 101157530
EDAT- 2013/12/04 06:00
MHDA- 2013/12/04 06:01
CRDT- 2013/12/04 06:00
PHST- 2013/12/04 06:00 [entrez]
PHST- 2013/12/04 06:00 [pubmed]
PHST- 2013/12/04 06:01 [medline]
AID - 10.1021/jp409497z [doi]
PST - ppublish
SO  - J Phys Chem B. 2013 Dec 27;117(51):16577-86. doi: 10.1021/jp409497z. Epub 2013 
      Dec 12.