U.S. patent application number 15/240975 was filed with the patent office on 2018-02-22 for ternary glass materials with low refractive index variability.
The applicant listed for this patent is LOCKHEED MARTIN CORPORATION, University of Central Florida Research Foundation, Inc.. Invention is credited to Clara Rivero BALEINE, Benn H. GLEASON, Kathleen A. RICHARDSON, Jeffrey Linn RUCKMAN.
Application Number | 20180050955 15/240975 |
Document ID | / |
Family ID | 61191213 |
Filed Date | 2018-02-22 |
United States Patent
Application |
20180050955 |
Kind Code |
A1 |
BALEINE; Clara Rivero ; et
al. |
February 22, 2018 |
TERNARY GLASS MATERIALS WITH LOW REFRACTIVE INDEX VARIABILITY
Abstract
Ternary chalcogenide glass materials containing germanium can
display enhanced properties compared to corresponding binary
chalcogenide glass materials lacking germanium. For instance,
ternary chalcogenide glass materials containing germanium, arsenic
and selenium can exhibit improved Vickers micro-hardness values and
other enhanced mechanical properties while still maintaining small
changes in refractive index as function of temperature. Such
ternary glass materials can have a formula of
(As.sub.ySe.sub.z).sub.[(100-x)0.01]Ge.sub.x, in which x ranges
between about 1 and 5, y ranges between about 30 and 40, z ranges
between about 60 and 70, and y+z=100. Methods for producing the
ternary glass materials can include blending arsenic, selenium, and
germanium as a melt, and cooling the melt to form the ternary glass
material.
Inventors: |
BALEINE; Clara Rivero;
(Orlando, FL) ; GLEASON; Benn H.; (Tucson, AZ)
; RICHARDSON; Kathleen A.; (Geneva, FL) ; RUCKMAN;
Jeffrey Linn; (Orlando, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LOCKHEED MARTIN CORPORATION
University of Central Florida Research Foundation, Inc. |
Bethesda
Orlando |
MD
FL |
US
US |
|
|
Family ID: |
61191213 |
Appl. No.: |
15/240975 |
Filed: |
August 18, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03B 25/02 20130101;
C03C 3/321 20130101 |
International
Class: |
C03C 3/32 20060101
C03C003/32; C03B 25/02 20060101 C03B025/02 |
Claims
1. A composition comprising a ternary glass material, the ternary
glass material having a formula of
(As.sub.ySe.sub.z).sub.[(100-x)0.01]Ge.sub.x; wherein x ranges
between about 1 and 5, y ranges between about 30 and 40, z ranges
between about 60 and 70, and y+z=100.
2. The composition of claim 1, wherein the ternary glass material
has an index of refraction that varies by less than about 20
ppm/.degree. C.
3. The composition of claim 2, wherein the ternary glass material
is heated and cooled multiple times below the glass transition
temperature until the index of refraction remains substantially
unchanged at a given temperature.
4. The composition of claim 1, wherein the ternary glass material
has a transmission window of at least about 1 micron to about 12
microns.
5. The composition of claim 1, wherein the ternary glass material
has a Vickers micro-hardness of about 1.5 GPa or greater at a 100
mN load.
6. The composition of claim 1, wherein y ranges between about 30
and 35 and z ranges between about 65 and 70.
7. The composition of claim 1, wherein y ranges between about 35
and 40 and z ranges between about 60 and 65.
8. The composition of claim 1, wherein x ranges between about 1 and
3, y ranges between about 32.5 and 35, and z ranges between about
65 and 67.5.
9. The composition of claim 1, wherein x ranges between about 3 and
5, y ranges between about 30 and 32.5, and z ranges between about
67.5 and 70.
10. The composition of claim 1, wherein x ranges between about 4
and 5, y ranges between about 30 and 31, and z ranges between about
69 and 70.
11. The composition of claim 1, wherein the ternary glass material
consists essentially of about 29.7-39.6 atomic percent arsenic,
about 59.4-69.3 atomic percent selenium, and about 1-5 atomic
percent germanium.
12. An optical structure comprising the composition of claim 1.
13. A method comprising: blending a mixture comprising about
29.7-39.6 atomic percent arsenic, about 59.4-69.3 atomic percent
selenium, and about 1-5 atomic percent germanium as a melt; and
cooling the melt to form a ternary glass material.
14. The method of claim 13, further comprising: performing a first
annealing cycle in which the ternary glass material is heated to a
temperature below the glass transition temperature and then cooled;
and performing one or more subsequent annealing cycles until the
refractive index of the ternary glass material remains
substantially unchanged at a given temperature from that of a prior
annealing cycle.
15. The method of claim 13, wherein the ternary glass material has
a formula of (As.sub.ySe.sub.z).sub.[(100-x)0.01]Ge.sub.x; wherein
x ranges between about 1 and 5, y ranges between about 30 and 40, z
ranges between about 60 and 70, and y+z=100.
16. The method of claim 15, wherein y ranges between about 30 and
35 and z ranges between about 65 and 70.
17. The method of claim 15, wherein y ranges between about 35 and
40 and z ranges between about 60 and 65.
18. The method of claim 15, wherein x ranges between about 1 and 3,
y ranges between about 32.5 and 35, and z ranges between about 65
and 67.5.
19. The method of claim 15, wherein x ranges between about 3 and 5,
y ranges between about 30 and 32.5, and z ranges between about 67.5
and 70.
20. The method of claim 15, wherein x ranges between about 4 and 5,
y ranges between about 30 and 31, and z ranges between about 69 and
70.
21. The method of claim 13, wherein the ternary glass material
consists essentially of arsenic, selenium, and germanium.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
FIELD
[0003] The present disclosure generally relates to glass materials
and, more specifically, to glass materials having low refractive
index variability with temperature, improved mechanical strength in
some instances, and a wide transmission window.
[0004] BACKGROUND
[0005] Binary chalcogenide glasses can be present in a number of
optical systems, such as those employing infrared imaging. Although
binary chalcogenide glasses can be desirable due to their wide
transmission window in the infrared region of the electromagnetic
spectrum, these glass materials can present a number of challenges
that are not easily overcome. Many binary chalcogenide glasses
exhibit significant variation in their refractive index as a
function of temperature, and certain binary chalcogenide glasses
have a coefficient of thermal expansion (CTE) that is mismatched
with common metals used in the housings of optical systems, such as
aluminum. Since many optical systems employing binary chalcogenide
glasses are expected to operate over a wide temperature range,
these shortcomings can result in significant performance issues.
For example, thermal variation in the refractive index can result
in image distortion if imaging is not conducted at the optimal
temperature of a lens. Similarly, CTE mismatch can lead to
mechanical failure at extreme operating temperatures if expansion
rates are significantly different. In addition, many of the binary
chalcogenide glasses that do exhibit desirable optical properties
have poor thermo-mechanical robustness, such as unacceptable
softness and low glass transition temperatures.
[0006] AMTIR-5 (Amorphous Materials, Inc.) is among the binary
chalcogenide glass compositions described in U.S. Pat. No.
6,984,598. Although this binary chalcogenide glass exhibits low
refractive index variability with temperature, it has poor
mechanical properties and a relatively low glass transition
temperature, both of which can be problematic for incorporating
this glass material in various optical systems, especially those
intended for deployment in extreme operating environments.
[0007] Ternary glass compositions are also commercially available.
AMTIR-1 (Ge.sub.33As.sub.12Se.sub.55-Amorphous Materials, Inc.) and
IRG 24 (Ge.sub.10As.sub.40Se.sub.50-Schott) are illustrative
examples. However, the variation in refractive index with
temperature remains rather high for these materials as well.
[0008] In view of the foregoing, optical materials having low
refractive index variability as a function of temperature in
combination with improved mechanical properties would be of
considerable interest in the art. The present disclosure satisfies
the foregoing need and provides related advantages as well.
SUMMARY
[0009] In various embodiments, the present disclosure provides
compositions containing a ternary glass material, in which the
ternary glass material has a formula of
(As.sub.ySe.sub.z).sub.[(100-x)0.01]Ge.sub.x
in which x ranges between about 1 and 5, y ranges between about 30
and 40, z ranges between about 60 and 70, and y+z=100.
[0010] In other various embodiments, the present disclosure
provides optical structures containing a composition including a
ternary glass material having a formula of
(As.sub.ySe.sub.z).sub.[(100-x)0.01]Ge.sub.x
in which x ranges between about 1 and 5, y ranges between about 30
and 40, z ranges between about 60 and 70, and y+z=100.
[0011] In still other various embodiments, the present disclosure
provides methods for producing a ternary glass material. The
methods include blending a mixture containing about 29.7-39.6
atomic percent arsenic, about 59.4-69.3 atomic percent selenium,
and about 1-5 atomic percent germanium as a melt, and cooling the
melt to form a ternary glass material.
[0012] The foregoing has outlined rather broadly the features of
the present disclosure in order that the detailed description that
follows can be better understood. Additional features and
advantages of the disclosure will be described hereinafter. These
and other advantages and features will become more apparent from
the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] For a more complete understanding of the present disclosure,
and the advantages thereof, reference is now made to the following
descriptions to be taken in conjunction with the accompanying
drawings describing specific embodiments of the disclosure,
wherein:
[0014] FIGS. 1A and 1B show plots illustrating the variance of
refractive index as a function of composition for certain ternary
glass materials described herein;
[0015] FIGS. 2A and 2B show illustrative plots of refractive index
as a function of temperature for AMTIR-5 Control 2 over heating and
cooling cycles; and
[0016] FIGS. 3-8 show illustrative plots of refractive index as a
function of temperature for Ternary Glass Materials 1-6,
respectively.
DETAILED DESCRIPTION
[0017] The present disclosure is directed, in part, to compositions
including a ternary glass material containing arsenic, selenium and
germanium. The present disclosure is also directed, in part, to
lenses and other optical structures incorporating a ternary glass
material containing arsenic, selenium and germanium. The present
disclosure is also directed, in part, to methods for producing
ternary glass materials containing arsenic, selenium and
germanium.
[0018] As discussed above, binary chalcogenide glasses can be
desirable for their relatively low refractive index variability as
a function of temperature and their wide transmission window in the
infrared region of the electromagnetic spectrum. The low refractive
index variability and wide transmission window can make these
glasses suitable for use in various types of optical systems, such
as infrared imaging systems. However, binary chalcogenide glasses
can exhibit sub-optimal mechanical properties, such as limited
mechanical strength and coefficient of thermal expansion mismatch
issues, which can limit their applicability in extreme operating
conditions. Commercially available ternary chalcogenide glasses are
believed to be similarly limited.
[0019] As used herein, the terms "index of refraction," "refractive
index," and "index" synonymously refer to the velocity of
electromagnetic wave propagation in a medium relative to the speed
of light in a vacuum. The refractive index, n, is defined according
to Formula 1, where c is the speed of light in a vacuum and v is
the velocity of the electromagnetic radiation in a given
medium.
n=c/v (1)
Accordingly, the slower the velocity of electromagnetic wave
propagation in a given medium, the larger the refractive index
becomes.
[0020] The present inventors discovered that the properties of
binary chalcogenide glasses, particularly arsenic-selenium binary
chalcogenide glasses having limited refractive index variability as
a function of temperature, can be significantly enhanced by forming
ternary chalcogenide glasses. Specifically, the inventors
surprisingly discovered that by incorporating small amounts of
germanium into chalcogenide glass blends that are otherwise binary
in nature, the mechanical properties of the resulting ternary glass
material can be significantly enhanced. Advantageously, such
ternary glass materials can maintain the limited refractive index
variability with temperature and wide transmission window of the
parent binary chalcogenide glasses. Thus, the ternary glass
materials disclosed herein can be beneficially incorporated in
various types of optical systems, particularly those intended to
operate in the infrared region of the electromagnetic spectrum.
Although ternary chalcogenide glasses containing germanium, arsenic
and selenium are known, they contain considerably lower atomic
ratios of selenium and considerably higher atomic ratios of
germanium than do the ternary glass materials described herein.
[0021] More specifically, the inventors discovered that
compositions incorporating ternary glass materials containing
arsenic and selenium and between about 1 to 5 atomic percent
germanium provide improved mechanical properties compared to
compositionally similar binary chalcogenide glasses. Depending upon
the particular formulation of the ternary glass material, the glass
transition temperature can to increase up to about 9%, the
coefficient of thermal expansion can decrease by about 9%, and the
micro-hardness can increase by about 25%. Optimization, balancing
and even further enhancement of these properties can be realized
through tailoring of the particular composition of the ternary
glass material.
[0022] The inventors also discovered that a hysteresis can occur in
the refractive index variability as a function of temperature
depending upon how the ternary glass materials are processed. The
inventors specifically discovered that as-produced ternary glass
materials of the present disclosure initially exhibited different
refractive index values at various temperature points during a
heating cycle and subsequent cooling cycle. Similar behavior was
found to occur in AMTIR-5 and similar binary chalcogenide glasses.
The inventors further discovered that the hysteretic behavior could
be substantially eliminated or minimized, thereby stabilizing the
refractive index variability, by annealing either type of glass
material below the glass transition temperature, cooling and
repeating over multiple heating and cooling cycles until similar
refractive index values were observed at each measurement
temperature during the heating and subsequent cooling. Accordingly,
the refractive index variability with temperature became more
consistent following the multiple heating and cooling cycles,
thereby providing more consistent optical behavior over long-term
deployment at a variety of temperatures. Therefore, the inventors
discovered a relatively simple technique to stabilize the
refractive index variability of various types of chalcogenide
glasses, which can make them even more suitable for incorporation
in various optical systems and improve the performance thereof
[0023] When the term "about" is used herein in reference to a
range, both the upper endpoint of the range and the lower endpoint
of the range should be understood to be modified by this term. For
example, the phrase "about A to B" should be understood to present
a range of about A to about B.
[0024] In various embodiments, compositions described herein
include a ternary glass material containing or consisting
essentially of about 1-5 atomic percent germanium, about 29.7-39.6
atomic percent arsenic, and about 59.4-69.3 atomic percent
selenium. As used herein, the terms "glass" or "glass material"
refer to any amorphous (i.e., at least partially non-crystalline)
material that can reversibly transition from a molten state at high
temperatures to a hardened state at low temperatures, while
exhibiting a thermodynamic glass transition. Although silicate
glasses are most commonly associated with the term "glass," where
oxygen is a significant constituent, the term is to be construed
more broadly herein in view of the foregoing definition. Non-oxide
glasses, such as those disclosed herein, are also fully consistent
with the foregoing definition of the term "glass."
[0025] FIGS. 1A and 1B show plots illustrating the variance of
refractive index as a function of composition for certain ternary
glass materials described herein. The grayscale contours represent
the observed refractive index variance at a wavelength of 4.5
microns. FIG. 1B highlights the approximate composition region of
the ternary glass materials of the present disclosure. As can be
seen from FIGS. 1A and 1B, the composition region encompassing the
ternary glass materials of the present disclosure offers very low
refractive index variance as a function of temperature.
[0026] More specifically, compositions of the present disclosure
include a ternary glass material, in which the ternary glass
material has a formula of
(As.sub.ySe.sub.z).sub.[(100-x)0.01)]Ge.sub.x,
in which x ranges between about 1 and 5, y ranges between about 30
and 40, z ranges between 60 and 70, and y+z=100 The values of x, y
and z can be any integer or non-integer value within the foregoing
ranges. Accordingly, in the ternary glass materials of the present
disclosure, germanium substitutes for at least a portion of the
arsenic and/or selenium in binary glass materials of the form
As.sub.ySe.sub.z, in which y and z are within the ranges mentioned
above.
[0027] In more specific embodiments, y can range between about 30
and 35, and z can range between about 65 and 70. In further more
specific embodiments, x can range between about 1 and 3, y can
range between about 32.5 and 35, and z can range between about 65
and 67.5; or x can range between about 3 and 5, y can range between
about 30 and 32.5, and z can range between about 67.5 and 70; or x
can range between about 4 and 5, y can range between about 30 and
31, and z can range between about 69 and 70.
[0028] In other various specific embodiments, y can range between
about 35 and 40, and z can range between about 60 and 65. In still
other various specific embodiments, x can range between about 1 and
about 3, or between about 2 and about 3.5.
[0029] As indicated above, the various ternary glass materials
described can display any number of improved properties compared to
binary chalcogenide glasses of otherwise similar composition but
lacking germanium. Depending upon their particular composition, the
ternary glass materials of the present disclosure can display one
or more properties such as, for example: an index of refraction
that varies by less than about 20 ppm/.degree. C. or less than
about 10 ppm/.degree. C., having a transmission window of at least
about 1 micron to about 12 microns, and/or a Vickers micro-hardness
of about 1.5 GPa or greater at a 100 mN load. Suitable measurement
conditions and techniques for these features will be familiar to
one having ordinary skill in the art. Specific ternary glass
materials demonstrating one or more of these properties will be
further illustrated in the examples below.
[0030] In some embodiments, various addends can be included in the
ternary glass materials to form a composite. Suitable addends are
not considered to be particularly limited and can include fibers,
nanoparticles, quantum dots, and the like.
[0031] In some or other embodiments, the ternary glass material can
be heated and cooled multiple times below the glass transition
temperature until the index of refraction remains substantially
unchanged at a given temperature. That is, as alluded to above,
ternary glass materials of a given composition can be thermally
processed in order to stabilize the variance of their refractive
index as a function of temperature, thereby minimizing hysteretic
behavior. As-produced binary and ternary chalcogenide glasses that
have not been thermally processed in the manner described herein
are not believed to possess a stabilized index of refraction
profile.
[0032] In certain embodiments, the present disclosure provides
optical structures incorporating a composition containing a ternary
glass material, in which the ternary glass material has a formula
of
(As.sub.ySe.sub.z).sub.[(100-x)0.01)]Ge.sub.x,
in which x ranges between about 1 and 5, y ranges between about 30
and 40, z ranges between 60 and 70, and y+z=100. In some
embodiments, the optical structure can constitute a lens. Lenses
incorporating the ternary glass materials described herein can be
advantageous due to their broad transmission windows and enhanced
mechanical properties, as discussed above. Other types of optical
structures can also benefit from incorporation of the ternary glass
materials described herein. Illustrative optical structures in
which the presently described ternary glass materials can be
incorporated include, for example, lenses, mirrors, optical fibers,
optical coatings, waveguides, transformation optical components,
integrated circuit optics, metamaterial optics, volume gratings,
spectral filters, hybrid diffractive optical components, focal
plane array optics, hybrid refractive optical components, solar
collection optics, and the like.
[0033] In some embodiments, a metal can be in contact with the
ternary glass material in the optical structure. In some
embodiments, the metal can be aluminum. At least some of the
ternary glass materials described herein can be advantageous in
this regard, since they have coefficient of thermal expansion
values that are similar to that of aluminum. Other metals can be
chosen for use in conjunction with a particular ternary glass
material to accommodate its coefficient of thermal expansion value,
if necessary.
[0034] In still other various embodiments, the present disclosure
provides methods for producing compositions incorporating a ternary
glass material containing germanium. In various embodiments,
methods of the present disclosure can include blending a mixture
containing about 29.7-39.6 atomic percent arsenic, about 59.4-69.3
atomic percent selenium, and about 1-5 atomic percent germanium as
a melt, and cooling the melt to form a ternary glass material. As
indicated above, in more specific embodiments, the ternary glass
material can have a formula of
(As.sub.ySe.sub.z).sub.[(100-x)0.01)]Ge.sub.x,
in which x ranges between about 1 and 5, y ranges between about 30
and 40, z ranges between 60 and 70, and y+z=100. Still more
specific ranges for x, y and z are described in more detail
hereinabove.
[0035] In more specific embodiments, batching of the arsenic,
selenium, and germanium can take place together in an open silica
ampule while in an oxygen-deficient atmosphere (e.g., under vacuum
or using a blanket of inert gas). After evacuating using vacuum,
the ampule can be sealed using a torch. The sealed ampule can then
be ramped up to a melting temperature of about 700-800.degree. C.
for about 14-20 hours, for example in a rocking furnace. The melted
material can then be air quenched to room temperature, and then
annealed for several hours.
[0036] As also indicated hereinabove, the as-produced ternary glass
materials can display a hysteresis in their refractive index
variation as a function of temperature during heating and cooling
ramps. Specifically, at a given temperature, the as-produced
ternary glass materials can display different refractive index
values depending upon whether they are being heated or cooled. This
type of hysteretic behavior can be mitigated through performing one
or more heating and cooling cycles upon the as-produced ternary
glass material below its glass transition temperature. More
specifically, methods of the present disclosure can include
performing a first annealing cycle in which the ternary glass
material is heated to a temperature below the glass transition
temperature and then cooled, and performing one or more subsequent
annealing cycles until the refractive index of the ternary glass
material remains substantially unchanged at a given temperature
from that of a prior annealing cycle. That is, in some embodiments
of the present disclosure, multiple annealing cycles can be
performed until the refractive index variability at a given
temperature falls below a desired threshold value. In some
embodiments, one or two annealing cycles can be performed. In other
various embodiments, three annealing cycles, or four annealing
cycles, or five annealing cycles, or six annealing cycles, or seven
annealing cycles, or eight annealing cycles, or nine annealing
cycles, or ten annealing cycles can be performed. For example, in
some embodiments, a single additional annealing cycle to about
90.degree. C. with a one-hour hold can be performed.
[0037] Suitable techniques for forming the melt or for performing
the annealing cycle(s) are not considered to be particularly
limited in the various embodiments of the present disclosure.
Illustrative equipment can include, for example, ovens, autoclaves,
furnaces, lasers, and the like. The heating technique used to form
the melt and to perform the subsequent annealing cycles can be the
same or different.
[0038] In various embodiments, the melt can be shaped into various
forms before being cooled below the glass transition temperature
and solidified into the ternary glass material. Illustrative forms
can include for example, a rod, slab, fiber, preform, or a near net
shape lens that is subsequently further processed (e.g., through
polishing). In other embodiments, the melt can be layered upon an
optical substrate. The chosen form can be dependent upon the type
of optical structure into which the ternary glass material is
ultimately to be incorporated. Compatibility with subsequent
optical fabrication methodologies may also be considered.
EXAMPLES
[0039] Ternary glass materials having the compositions set forth in
Table 1 were formed by combining elemental forms of each component
and heating to form a melt. Batching of the components was
performed in an open silica ampule while in an oxygen deficient
atmosphere. Using a vacuum fitting and pump, the atmosphere was
evacuated from the silica ampule, and the ampule was sealed using
an oxygen gas torch. The sealed ampule was then placed in a rocking
furnace, and ramped up to a melting temperature of about
700-800.degree. C. for 14-20 hours. The melted material was then
air quenched to room temperature, and annealed for several hours.
The ternary glass materials were then annealed one or more times
below the glass transition temperature and cooled until the
refractive index at a given temperature was substantially unchanged
between subsequent annealing cycles.
TABLE-US-00001 TABLE 1 Ternary Glass Chemical Composition (atomic
percent) Material As Se Ge 1 34.475 64.025 1.5 2 34.2125 63.5375
2.25 3 33.95 63.05 3.0 4 31.525 65.475 3.0 5 28.8 67.2 4.0 6 28.65
66.85 4.5
[0040] Physical property measurements were conducted through
appropriate techniques and compared to two AMTIR-5 controls. The
first AMTIR-5 control (AMTIR-5 Control 1) represents literature
values of the as-produced binary glass material. The second AMTIR-5
control (AMTIR-5 Control 2) was processed with multiple annealing
cycles until the refractive index became substantially constant at
a given temperature during heating and subsequent cooling. AMTIR-5
Control 2 values represent the average of two multiply annealed
samples. Table 2 summarizes the physical property measurements of
Ternary Glass Materials 1-6 and the two AMTIR-5 controls.
TABLE-US-00002 TABLE 2 AMTIR-5 Controls Control Control Ternary
Glass Materials Physical Property 1 2 1 2 3 4 5 6 Transmission
1.0-12 1.0-12 1.0-12 1.0-12 1.0-12 1.0-12 1.0-12 1.0-12 Window
(.mu.m) Refractive Index 2.7545 2.7564 2.7256 2.7213 2.7211 2.6817
2.6538 2.6553 (4.515 .mu.m, 30.degree. C.) dn/dT
(.times.10.sup.-6/.degree. C.) <1 20.2 19.0 28.5 40.0 19.5 -1.8
6.0 (4.515 .mu.m) T.sub.g (.degree. C.) 143 169 171 177 184 164 166
166 CTE (ppm/.degree. C.) 23.7 25.6 23.4 23.8 23.5 22.3 26.0 25.2
Density (g/cm.sup.3) 4.51 4.63 4.55 4.56 4.56 4.54 4.57 4.52
Micro-hardness, 0.735 1.297 1.54 1.53 1.61 1.49 1.58 1.53 H.sub.v,
(GPa, 100 mN load)
[0041] FIGS. 2A and 2B show illustrative plots of refractive index
as a function of temperature for AMTIR-5 Control 2 over heating and
cooling cycles. FIG. 2A shows the refractive index variance with
temperature during the first heating and cooling cycle, and FIG. 2B
shows the refractive index variance with temperature during the
second heating and cooling cycle. In FIG. 2A, the forward and
reverse curves of refractive index variance with temperature did
not mirror one another. That is, there was a hysteresis. In
contrast, FIG. 2B showed much less variance between the forward and
reverse curves during the second heating cycle. The increase in
refractive index as a function of temperature was approximately
linear.
[0042] FIGS. 3-8 show illustrative plots of refractive index as a
function of temperature for Ternary Glass Materials 1-6,
respectively. These samples were similarly annealed one or more
times below their glass transition temperatures to stabilize the
refractive index variance as a function of temperature. Like the
AMTIR-5 control, these samples likewise produced approximately
linear variance of the refractive index as a function of
temperature. As can be seen from FIGS. 7 and 8, Ternary Glass
Materials 5 and 6 both provided desirably low refractive index
variance below 10 ppm/.degree. C.
[0043] Although the disclosure has been described with reference to
the above embodiments, one of ordinary skill in the art will
readily appreciate that these are only illustrative of the
disclosure. It should be understood that various modifications can
be made without departing from the spirit of the disclosure. The
disclosure can be modified to incorporate any number of variations,
alterations, substitutions or equivalent arrangements not
heretofore described, but which are commensurate with the spirit
and scope of the disclosure. Additionally, while various
embodiments of the disclosure have been described, it is to be
understood that aspects of the disclosure may include only some of
the described embodiments. Accordingly, the disclosure is not to be
seen as limited by the foregoing description.
* * * * *