Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Temperature
Reexamination Certificate
2002-08-27
2004-06-01
Wilson, Allan R. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Temperature
C136S205000
Reexamination Certificate
active
06744110
ABSTRACT:
The invention relates to thermoelectrically active materials, as well as to generators and Peltier arrangements containing them.
Thermoelectric generators per se have been known for a long time. p- or n-doped semiconductors, which are heated on one side and are cooled on the other side, transport electrical charges through an external circuit, with electrical work being done at a load in the circuit. The efficiency achieved in this case for the conversion of heat into electrical energy is limited thermodynamically by the Carnot efficiency. For instance, with a temperature of 1000 K on the hot side and 400 K on the “cold” side, an efficiency of (1000-400): 1000=60% would be possible. Unfortunately, efficiencies of only up to 10% have been achieved to date.
On the other hand, if a direct current is applied to such an arrangement, then heat will be transported from one side to the other. Such a Peltier arrangement works as a heat pump and is therefore suitable for the cooling of equipment parts, vehicles or buildings. Heating by means of the Peltier principle is also more favorable than conventional heating, because the quantity of heat transported is always greater than corresponds to the energy equivalent which is supplied.
A good review of effects and materials is given e.g. by Cronin B. Vining, ITS Short Course on Thermoelectricity, Nov. 8, 1993, Yokahama, Japan.
Thermoelectric generators are currently used in space probes for the generation of direct currents, for the cathodic corrosion protection of pipelines, for the energy supply of lighted and radio buoys, and for the operation of radios and television sets. The advantages of thermoelectric generators are that they are extremely reliable, they work irrespective of atmospheric conditions such as humidity, and no material transport susceptible to disruption takes place, instead only charge transport; the fuel is burned continuously—and catalytically without a free flame—so that minor amounts of CO, NO
x
and unburned fuel are released; it is possible to use any fuels from water through natural gas, gasoline, kerosene and diesel to biologically produced fuels such as rapeseed oil methyl ester.
Thermoelectric energy conversion therefore fits in extremely flexibly with future requirements such as hydrogen economy or energy production from regenerative energies.
An especially attractive application could involve use for conversion into electrical energy in electrically powered vehicles. No modification to the existing network of the fuelling stations would need to be carried out. For such an application, however, efficiencies in excess of 30% would be necessary.
The conversion of solar energy directly into electrical energy could also be very attractive. Concentrators such as parabolic collectors can focus the sun's energy with efficiencies of 95-97% onto thermoelectric generators, so that electrical energy can be produced.
Higher efficiencies, however, are necessary for use as a heat pump.
It is an object of the present invention to provide thermoelectric active materials which permit higher efficiencies than previously. A characteristic of thermoelectric materials is the so-called Z factor (figure of merit)
Z
=
α
2
*
σ
K
with &agr; being the Seebeck coefficient, &sgr; being the electrical conductivity and K being the thermal conductivity.
A more accurate analysis is the efficiency as &eegr;
η
=
T
high
-
T
low
T
high
*
M
-
1
M
+
T
high
T
low
with M=[1+z/2(T
high
−T
low
)1/2
(cf. Mat Sci. and Eng. B29 (1995) 228).
The aim is therefore to provide a material having a maximally high value for Z and high achievable temperature difference. In terms of solid-state physics, many problems need to be overcome in this case:
A high &agr; entails high electron mobility in the material; i.e. electrons (or holes in the case of p-conducting materials) must not be strongly bound to the atom rumps. Materials having a high electrical conductivity usually also have a high thermal conductivity (Wiedemann-Franz law), so that Z cannot be favorably influenced. Currently used materials such as Bi
2
Te
3
, PbTe or SiGe indeed represent compromises. For instance, the electrical conductivity is reduced less than the thermal conductivity by alloying. It is therefore preferable to use alloys such as e.g.(Bi
2
Te
3
)
90
(Sb
2
Te
3
)
5
(Sb
2
Se
3
)
5
or Bi
12
Sb
23
Te
65
, as are described in U.S. Pat. No. 5,448,109.
For thermoelectric materials with high efficiency, it is also preferable to satisfy further constraints. Above all, they must be thermally stable so that they can work for years without substantial loss of efficiency at working temperatures of 1000 to 1500 K. This entails phases which per se are stable at high temperatures, a stable phase composition, as well as negligible diffusion of alloy constituents into the adjoining contact materials.
The recent patent literature contains descriptions of thermoelectric materials, for example U.S. Pat. No. 6,225,550 and EP-A-1 102 334. U.S. Pat. No. 6,225,550 relates essentially to materials constituted by Mg
x
Sb
z
, which are additionally doped with a further element, preferably a transition metal.
EP-A-1 102 334 discloses p- or n-doped semiconductor materials which represent an at least ternary material constituted by the material classes: silicides, borides, germanides, tellurides, sulfides and selenides, antimonides, plumbides and semiconducting oxides.
There is nevertheless still a need for thermoelectrically active materials which have a high efficiency and exhibit a suitable property profile for different application fields. Research in the field of thermoelectrically active materials can by no means yet be regarded as concluded, so that there is still a demand for different thermoelectric materials.
We have found that this object is achieved by a thermoelectric generator or a Peltier arrangement having a thermoelectrically active semiconductor material constituted by a plurality of metals or metal oxides, wherein the thermoelectrically active material is selected from a p- or n-doped semiconductor material constituted by a ternary compound of the general formula (I)
Me
x
S
A
y
S
B
z
(I)
with
Me=Al, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu or Ag,
S
A
,S
B
=B, C, Si, Ge, Sb, Se or Te,
where S
A
and S
B
respectively come from different groups of the periodic table,
x, y, z independently of one another have values from 0.01 to 1,
and where the proportion by weight of S
A
and S
B
together is no more than 30%, expressed in terms of the total semiconductor material,
except for ternary compounds constituted by AlB
12
and SiB
6
,
or a mixed oxide of the general formula (II)
[
(
CaO
)
u
·
(
SrO
)
v
·
(
BaO
)
w
·
(
1
/
2
Bi
2
O
3
)
x
]
f
·
2
n
+
a
2
·
(
{
k
}
Me
n
O
n
2
·
{
2
-
k
}
Me
n
+
a
O
n
+
a
2
)
(
II
)
with
Me=Fe, Cu, V, Mn, Sn, Ti, Mo, W
n=integer from 1 to 6,
a=1 or 2,
f=number from 0.2 to 5,
k=number from 0.01 to 2, preferably 0.01 to 1.99, e.g. 1
u+v+w+x=1.
The thermoelectric generators and Peltier arrangements according to the invention enhance quite generally, on the one hand, the range of available thermoelectric generators and Peltier arrangements. Owing to the different chemical systems, it is possible to satisfy different requirements in various application fields of the thermoelectric generator or Peltier arrangements. The thermoelectric generators and Peltier arrangements according to the invention hence significantly extend the possibilities for application of these elements under different conditions.
Preferred semiconductor materials will be explained in more detail below.
In the ternary compounds of the general formula (I), S
A
and S
B
are preferably selected from B, C, Ge, Sb and Te.
In this semiconductor material, Me is preferably selected from one of the following groups:
1) Al, Ti, Zr.
2) V, Nb, Ta
3) Cr, Mo, W
4) Mn, Fe, Co, Ni
5) Cu, A
Kühling Klaus
Sterzel Hans-Josef
BASF - Aktiengesellschaft
Keil & Weinkauf
Wilson Allan R.
LandOfFree
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