“…The fit (Table 2) yields a Li-O coordination number of 3.9(1). This result is in close agreement with the lithium coordination number of 4 in crystalline Li2Te2O5 [22] and Li2TeO3 [16]. The Li-O peak in ΔT(r)Na19-Li20 overlaps with the shorter Na-O bond lengths.…”
Section: The Isostoichiometric Difference Methodsupporting
confidence: 84%
“…To interpret the results, an assumed K environment of 3 oxygen atoms at 2.67 Å and 4 oxygen atoms at 2.88 Å was used [5]. Finally, a series of Reverse Monte Carlo (RMC) simulations of neutron and X-ray diffraction data for lithium, sodium and potassium tellurites has been performed [3], but the local environment of the alkali atoms was not determined; instead information from related crystal structures (Na2Te4O9 [20], K2Te4O9 [21], Li2Te2O5 [22]) was used to constrain the coordination numbers and bond lengths of the alkali ions, in order to calculate the Te-O bond distribution for Li, Na and K modified glasses.…”
Neutron diffraction measurements are reported for five binary alkali tellurite glasses, xM2O·(100-x)TeO2 (containing 10 and 20 mol% K2O, 10 and 19 mol% Na2O, and 20 mol% 7 Li2O), together with 23 Na MAS NMR measurements for the sodium containing glasses.Differences between neutron correlation functions are used to extract information about the local environments of lithium and sodium. The Na-O bond length is 2.37(1) Å and the average Na-O coordination number, nNaO, decreases from 5.2(2) for x=10 mol% Na2O to 4.6(1) for x=19 mol% Na2O. The average Li-O coordination number, nLiO, is 3.9(1) for the glass with x=20 mol% Li2O and the Li-O bond length is 2.078(2) Å. As x increases from 10 to 19 mol% Na2O, the 23 Na MAS NMR peak moves downfield, confirming an earlier report of a correlation of peak position with sodium coordination number. The close agreement of the maximum in the Te-O bond distribution for sodium and potassium tellurite glasses of the same composition, coupled with the extraction of reasonable alkali coordination numbers using isostoichiometric differences, gives strong evidence that the tellurium environment in alkali tellurites is independent of the size of the modifier cation used.
“…The fit (Table 2) yields a Li-O coordination number of 3.9(1). This result is in close agreement with the lithium coordination number of 4 in crystalline Li2Te2O5 [22] and Li2TeO3 [16]. The Li-O peak in ΔT(r)Na19-Li20 overlaps with the shorter Na-O bond lengths.…”
Section: The Isostoichiometric Difference Methodsupporting
confidence: 84%
“…To interpret the results, an assumed K environment of 3 oxygen atoms at 2.67 Å and 4 oxygen atoms at 2.88 Å was used [5]. Finally, a series of Reverse Monte Carlo (RMC) simulations of neutron and X-ray diffraction data for lithium, sodium and potassium tellurites has been performed [3], but the local environment of the alkali atoms was not determined; instead information from related crystal structures (Na2Te4O9 [20], K2Te4O9 [21], Li2Te2O5 [22]) was used to constrain the coordination numbers and bond lengths of the alkali ions, in order to calculate the Te-O bond distribution for Li, Na and K modified glasses.…”
Neutron diffraction measurements are reported for five binary alkali tellurite glasses, xM2O·(100-x)TeO2 (containing 10 and 20 mol% K2O, 10 and 19 mol% Na2O, and 20 mol% 7 Li2O), together with 23 Na MAS NMR measurements for the sodium containing glasses.Differences between neutron correlation functions are used to extract information about the local environments of lithium and sodium. The Na-O bond length is 2.37(1) Å and the average Na-O coordination number, nNaO, decreases from 5.2(2) for x=10 mol% Na2O to 4.6(1) for x=19 mol% Na2O. The average Li-O coordination number, nLiO, is 3.9(1) for the glass with x=20 mol% Li2O and the Li-O bond length is 2.078(2) Å. As x increases from 10 to 19 mol% Na2O, the 23 Na MAS NMR peak moves downfield, confirming an earlier report of a correlation of peak position with sodium coordination number. The close agreement of the maximum in the Te-O bond distribution for sodium and potassium tellurite glasses of the same composition, coupled with the extraction of reasonable alkali coordination numbers using isostoichiometric differences, gives strong evidence that the tellurium environment in alkali tellurites is independent of the size of the modifier cation used.
“…In tellurite glasses formed with less than 50% M 2 O, a variety of structures, such as TeO 3/2 O - , TeO 1/2 O 2 - , and so forth have been postulated (Figure ). ,, To evaluate the likelihood of these structures in glasses, it is helpful to consider crystal phases of similar composition. These are known to exist at 20% M 2 O for M = Na , K, and Cs and at 33% M 2 O for Li, Na, K, and Cs. , The Li- and Cs-based structures have been determined previously. , Recently, we succeeded in solving both Na structures. , 1 Structures found in tellurites. (a) the basic trigonal bipyramidal unit, with the lone pair occupying one of the equatorial sites.…”
The crystal structures of potassium tetratellurite and potassium
ditellurite are reported, completing the series of
known phases of alkali tellurites including lithium, sodium, potassium
and cesium. Potassium tetratellurite
(K2Te4O9, a = 7.572(1) Å,
b = 17.821(3) Å, c = 7.829(1) Å,
β = 108.62°, monoclinic, P21/c,
Z = 4) contains
linked 12-membered tellurite rings, coordinated by potassium. The
ditellurite (K2Te2O5,
a = 5.454(1) Å, b =
15.142(1) Å, c = 7.731(1) Å, β =
93.71(1)°, Z = 4), monoclinic,
P21/a, Z = 4) consists
of infinite chains
separated by rough sheets of cations. Comparison of the different
alkali tellurite structures confirms the qualitative
picture that as alkali oxide is added, the tellurite network is
increasingly cleaved. We show, however, that the
extent of network cleavage depends significantly on the nature of the
modifying ion, with lithium inducing the
fewest nonbridging oxygens per equivalent and potassium and cesium
inducing as many as two nonbridging
oxygens per equivalent of added cation. This behavior is due to
the stability in tellurites of delocalized electrons
across several nonbridging oxygens and is contrasted with the much
simpler and well-known case of silicate
modification.
“…3. In order to identify these phases, observed DTA and DSC curves of 30Li 2 OÁ70TeO 2 powder sample in the temperature range 473±873 K. at high temperatures, X-ray diffraction data of -Li 2 Te 2 O 5 were calculated from its single-crystal structure (Cachau-Herreillat et al, 1981) by using Crystal-Maker (Palmer, 1996). This is necessary because there is no relevant X-ray diffraction data ®le in the JCPDS (International Centre for Diffraction Data) database.…”
Section: Identification Of the Phases Observedmentioning
confidence: 99%
“…Calculated X-ray pro®le of -Li 2 Te 2 O 5 based on a single-crystal structure (Cachau-Herreillat et al, 1981).…”
The thermal behaviour of a 30Li2O·70TeO2 glass was studied by use of an in situ high‐temperature X‐ray diffractometer equipped with a position‐sensitive detector (PSD). The dynamical structural changes were also observed by differential thermal analysis (DTA) and differential scanning calorimetry (DSC) measurements. Differences and contradictions exist in previous studies related to the phase relation at high temperature, including the process of phase change. It is found that in the exothermic process after a glass transition between 553 and 623 K, an unknown phase of lithium tellurite (LT‐X) crystallizes at first. At almost the same temperature, a minor component of vitreous TeO2 appears during decomposition of vitreous 30Li2O·70TeO2 of the initial phase. After that, the thermal changes of the lithium tellurite and the TeO2 components proceed independently. The LT‐X phase converts to α‐Li2Te2O5, and the vitreous TeO2 phase is followed by crystallization of an α‐TeO2 phase. In the endothermic process between 673 and 793 K, the α‐Li2Te2O5 phase transforms into a β‐Li2Te2O5 phase and the minor crystalline α‐TeO2 phase melts. Then, β‐Li2Te2O5 incongruently melts to form Li2TeO3 and a molten TeO2 phase. Li2TeO3 continuously melts at around 763 K. The results show a possibility of reversible change between the α‐Li2Te2O5 and the β‐Li2Te2O5 phases.
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